This summer, when the U.S. and Iran signed a temporary truce, China touted its role in easing tensions in the Middle East. It said its foreign ministry made dozens of calls to nudge peace along, and that President Xi Jinping himself had intervened with suggestions to end the fighting.

That same day, a plane from China landed in Tehran. It carried a shipment for Iran's Ministry of Defense that included electronics components that can be used to make parts for drones and missile guidance systems, according to Iranian customs data analyzed by The Wall Street Journal.

It was one of around 1,300 shipments that included "dual use" components from China to Iran's defense ministry this year through the end of June, customs data show. Two days after the electronics components shipment, there were more than a dozen other shipments carrying parts worth more than $6 million that can be used in drones.

Xi is visiting President Trump in Washington this week for a summit that will cover weighty topics including trade, artificial-intelligence safety and relations with Taiwan. But the elephant in the room will be China's continuing support for Iran.

China has become the only major buyer of Iranian oil, despite U.S. sanctions meant to stop the flows, providing billions of dollars for Tehran this year. Chinese front companies help launder the funds, while Chinese banks route the transactions through the country's financial plumbing, using China's currency, to evade U.S. oversight, U.S. officials and people familiar with the flows say.

On the battlefield, satellite imagery procured from Chinese entities has been linked by U.S. officials to an Iranian strike that killed three American troops, the Journal has reported. Chinese companies have also helped provide chemical precursors used to manufacture the types of ballistic missiles used in the attack, according to a document viewed by the Journal and people familiar with the matter.

The actions illustrate a level of Chinese support for Iran that hasn't been previously reported or publicly acknowledged by the Trump administration. That support has helped extend a conflict that is increasing global energy prices, draining weapons stockpiles and heaping pressure on Trump ahead of the midterm elections.

Beijing said it consistently abides by international rules and opposes "attempts to smear China by associating it with the conflict." It said China maintains cooperation with Iran and supports all efforts toward peace in the Middle East.

In the past, China has said it strictly regulates the export of dual-use components, which can serve both civilian and military purposes. It has said it rejects unilateral U.S. sanctions, including those that punish unauthorized trading of dual-use materials, saying the sanctions violate international law.

Iranian officials didn't respond to requests for comment.

Washington has launched hundreds of sanctions targeting Iran since the war began on Feb. 28, including penalties against companies and individuals in China it believes are helping Tehran. Those steps, along with an embargo of Iranian trade, have caused a contraction of Iran's economy.

But the White House has proven reluctant to more seriously confront Beijing over its support for Iran, which has continued launching attacks on U.S. forces and oil infrastructure in the Middle East. Trump has made improved relations with Beijing a priority after a tariff war last year showed China has options to hurt the U.S. economy, including restricting American access to rare earth materials.

Ahead of this week's summit, Trump told top officials and aides that maintaining good relations with Xi is a priority, people familiar with the discussions said. As a result, senior officials have repeatedly played down the significance of Chinese aid to Iran, avoiding criticism of Beijing that could jeopardize the meeting.

Many within the administration believe the reluctance to take on Beijing is weakening America's ability to pressure Tehran. Lawmakers on both sides of the political aisle have called on Trump to confront Xi more directly.

"There is now a large and growing body of evidence that Chinese companies are helping Iran target and kill American troops, keep Iran's drone and missile programs alive, and sustain Iran's economy," Sen. Elissa Slotkin, a Michigan Democrat, wrote in a letter to Trump on Friday that was shared with the Journal. She urged Trump to make Chinese support for Iran a "centerpiece" of his talks with Xi.

Trump brushed off concerns about Chinese support for Iran when asked earlier this month whether he would raise the issue with Xi. "I think he's behaved reasonably well, and we behave reasonably well," he said.

On Wednesday, Secretary of State Marco Rubio said the U.S. and China would have "a very frank conversation" at the Xi-Trump summit. "We'll talk about everything that's relevant. We'll talk about everything that's important," he said. "The idea that we would not interact with them at the highest levels is irresponsible."

A spokesperson for the Treasury Department said it maintains an active channel with Chinese counterparts and won't hesitate to act when warranted. "This administration has repeatedly targeted malign Iran-related activity that exploits or transits China's jurisdiction and will continue to do so," the spokesperson said.

The White House has said it is working aggressively to disrupt and penalize anyone who does business with the Iranian regime.

In backing Iran, Beijing hopes to undermine Washington's diplomatic standing and draw down U.S. weapons inventories, weakening it militarily, political analysts say. Yet China is also wary of going too far. It values economic ties with America, and as the world's largest energy importer, China suffers if the oil shock caused by the conflict drags on, political analysts say.

Air shipments

The shipments to Iran's defense ministry that were reviewed by the Journal are part of a surge in flights with cargo from China to Iran this year. The air bridge has become a crucial supply route for Iran's drone and ballistic-missile programs as the U.S. Navy blocks Iranian sea trade, defense experts say.

The shipments have arrived at Tehran's Imam Khomeini International Airport. The boxes are packed with GPS tracking devices, electric motors and aircraft engine parts, according to Iranian customs records provided by trade database ImportGenius.

Records from January 2025 to the end of June this year show thousands of shipments to Iran's defense ministry and Iranian companies of items that can be used to build drones and other weapons. Many of the entries are marked with a reference to "Article 119," a section in Iranian customs regulations that grants full tariff exemptions for armaments and defense imports.

China has offered economic and military support for Iran for decades. But the two sides deepened ties after the Trump administration in 2018 launched a "maximum pressure" campaign to cut Iranian oil exports to zero and force Iran to negotiate over its nuclear program.

The campaign included sanctions penalizing foreign entities that helped Iran, cutting them off from the U.S.-led global financial system.

Rejecting those rules, Tehran and Beijing signed a 25-year strategic pact in 2021. China became Iran's biggest oil importer, buying up more than 80% of its crude exports, according to U.S. lawmakers. An elaborate network of Chinese banks and Hong Kong shell companies evolved to help Iran evade sanctions and keep the oil flowing, the Journal has reported.

Hong Kong said it enforces United Nations sanctions but not those imposed unilaterally by nations, which it says violate international law.

Chinese exporters of dual-use goods and electronics also began attending trade fairs in Iran, translating their corporate slogans into Farsi to build local ties, according to an analysis of social-media posts by the Center for Strategic and International Studies in Washington.

In the following years, Chinese companies produced for Iran chemical materials such as sodium perchlorate, which is used to make propellant for ballistic missiles. The exports became more important for Iran after Israel largely destroyed its missile program in attacks in 2024, forcing the regime to replenish its arsenal.

The sales became widely known when the Journal and other media reported on them in 2025. U.S. forces later that year raided a ship carrying dual-use components from China to Iran, signaling that Washington was watching.

One Chinese company that attempted to sell chemical materials, Haokun Energy, told a U.S.-sanctioned importer of products for Iran last December that exports of sodium perchlorate required government licenses. It said it had coordinated with Chinese authorities "to process part of the licenses confidentially," Haokun wrote in a letter viewed by the Journal.

Treasury had earlier sanctioned Haokun and the importer for helping Iran sell oil to China. The December letter said Haokun had set up a Beijing-based shell company for the sodium perchlorate transaction. The Journal verified the company was established weeks before the letter's date. It couldn't be determined if the deal progressed.

Haokun didn't respond to requests for comment.

Material for Shaheds

Days before the U.S.-Iran war began, Iranian customs data showed a delivery of 300 tons of chemical compounds from China to Iran's ministry of defense.

Once the war started, trade between Iran and China initially collapsed, according to Iranian customs data and Kpler, a research firm that tracks oil shipments. The U.S. Navy blockade of Iranian ports, announced in April, further tightened the noose.

Tehran responded by expanding air links between China and Iran via Mahan Air, an Iranian airline sanctioned by the U.S. that Treasury says has ferried cash, weapons and personnel for Iran. The airline increased flights from Beijing, Shanghai and Guangzhou to Tehran to about 27 a week by the end of April from four at the start of March, according to FlightRadar24 data.

Air shipments to Iran's ministry of defense accelerated, customs data show. Mahan didn't respond to requests for comment.

Researchers who track trade with Iran say the shipments involve little-known Chinese suppliers working with Iranian importers. Some of the components on offer are known to be used to make Shahed drones, said Kate Koren, deputy director of the economics program at CSIS in Washington. The cheap but deadly Iranian drones have caused significant damage to U.S. bases.

In a soon-to-be-published report, Koren said she found several Chinese companies that had publicly advertised sales this year for sensitive electronics, including those found in the Shahed.

In May, Treasury sanctioned Chinese and Hong Kong-based companies it said were trying to help Iran acquire weapons, including shoulder-fired missile launchers. A video posted that month on Iran's Tasnim news agency, affiliated with the Islamic Revolutionary Guard Corps, or IRGC, showed members of the militia getting training on how to use the missile launchers, known as manpads, to shoot down U.S. fighter jets.

Iran currently operates manpads that it manufactures inside the country based on older Chinese versions, according to former Treasury officials. But Iranian officials want access to China's latest models, which are more effective, the former officials said.

Over the following weeks, U.S. officials sanctioned more Chinese individuals and companies for procuring weapons for Iran's military and the IRGC. One of the procurement networks tried to buy manpads for Iran's Center for Innovation and Technology Cooperation, which works to adapt foreign-made weapons to be produced at home, U.S. officials said.

The group tried to deliver the manpads to Iran via Belarus to obfuscate the Iranian end-user, but it wasn't successful, U.S. officials said.

'I trust them'

On June 17, the U.S. and Iran signed a 60-day truce. Days later, Iranian customs noted air shipments from China with more than $6 million of electronics components that the U.S. government has said are used for a variety of military purposes, including in flight control units for precision-guided weapons.

In July, the U.S. added new sanctions on individuals and companies working for Mahan Air, including a China-based company it said acted as a sales agent for the airline, coordinating the transport of electronics. The U.S. issued more than 100 additional sanctions that month.

But divisions were deepening within the administration over how hard to press China.

Defense Secretary Pete Hegseth told lawmakers in July that China, along with Russia, was enabling Iran "at different levels."

Days later, Trump pushed back. "I don't know that they're enabling," he said, insisting that Xi had personally assured him China wouldn't provide Iran with weapons.

"I trust them," he said of Xi and Russian President Vladimir Putin. "There could be some things they do. But thus far, at least, it has not been major."

The same week, after meeting Chinese Foreign Minister Wang Yi in Manila, Rubio told reporters that "nothing that China has done has in any way changed the trajectory" of the conflict. Beijing had in some instances been "quite cooperative," he said.

Behind the scenes, U.S. officials were trying to tighten the screws on support for Iran involving China. In one episode, U.S. officials identified sales of petrochemical products from Iran to Egypt, being paid for with U.S. dollars, violating U.S. sanctions.

The transactions were handled through the United Arab Emirates branch of Banque Misr, an Egyptian state-owned bank, according to several people familiar with the transactions. Treasury authorities sent warnings to the bank to stop, the people said.

Instead, Banque Misr switched the payments to China's yuan currency. They were to be cleared through the Cross-Border Interbank Payment System, a Chinese financial network in which transactions are harder for U.S. authorities to track, the people said.

The plans eventually failed, as U.S. officials became aware of them, communicating their disapproval to Egyptian officials, according to the people.

Treasury later went after Banque Misr, calling its U.A.E. branch "a critical node" for Tehran's financial activities and moving to cut its access to U.S. dollars.

Egypt's foreign ministry and Banque Misr said they were communicating with U.S. authorities about Treasury's allegations. Banque Misr added that it respects "relevant regulatory and legal frameworks."

The episode created tension between China and Egypt, with Beijing suspicious that Egyptian officials had shared information with the Americans, people aware of the details said. Xi himself brought the issue up in a summit with Egypt's president in Cairo earlier this month, one of the people added.

Satellite images

Some Trump officials and U.S. national security officials still thought the U.S. wasn't doing enough.

Concerns grew more urgent after U.S. officials concluded Iran had used Chinese satellite imagery before and after a July 17 strike that killed three U.S. troops, linking it directly to the attack. The Trump administration had already sanctioned three Chinese satellite-imagery companies in May for providing data it said could help Iran target U.S. forces.

In late August, Trump and Treasury Secretary Scott Bessent launched "Operation Economic Outcast," a program to "sever every economic lifeline" sustaining the Iranian regime.

The U.S. added sanctions against a China-owned oil tanker that transported Iranian oil and a network of Chinese companies and individuals that helped Iran obtain critical components. But no major Chinese companies were targeted.

When reporters twice asked Bessent whether the administration would strengthen sanctions against Chinese banks and businesses, Bessent declined to single out China, saying that "every country" should be prepared to face U.S. sanctions.

Although the U.S. blockade has made it much harder for Iran to export oil, some keeps flowing to China. About four million barrels were delivered to China in the week after "Operation Economic Outcast" was launched, according to Kpler calculations.

Mahan Air, meanwhile, flew from China to Iran 39 times in the first week of September, double its prewar level, according to FlightRadar24.

Many of the flights appear to be focused only on cargo, rather than moving passengers. Many tracked by FlightRadar24 in early September, for example, weren't available for booking on the airline's website.

Last week, Iranian state-affiliated media said Mahan would suspend flights to Oman and Turkey. But the airline continues to fly to China.