U.S. officials believe Chinese companies have been negotiating arms sales to Iran and plotting to route the weapons through third countries to disguise their origin, according to a report published Wednesday by The New York Times.

Citing unnamed U.S. officials briefed on the intelligence, the Times reported that American spy agencies have gathered information showing Chinese firms and Iranian officials have discussed transferring weapons through intermediary nations. At least one of the third countries is in Africa, officials told the newspaper. It is not clear whether any shipments have actually been delivered, and no Chinese-made arms have been observed on the battlefield since the war began.

U.S. officials said they do not believe the Chinese government has formally approved the arms transfers, but added that the talks were unlikely to have taken place without Beijing’s knowledge, the NYT said. 

The report comes as President Trump is visiting Beijing for a high-stakes summit with Chinese President Xi Jinping, raising pressure on the U.S. leader to confront his counterpart over Beijing’s support for Tehran in its war with Israel and the United States.

Trump told reporters Tuesday he planned to have a “long talk” with Xi about the Middle East conflict and said the Chinese leader had been “relatively good” on Iran, according to the newspaper After earlier reporting last month that China may have transferred shoulder-fired anti-aircraft missiles, known as MANPADS, to Iran, Trump said he had written to Xi asking him to halt such transfers. 

“I wrote him a letter asking him not to do that, and he wrote me a letter saying that, essentially, he’s not doing that,” Trump told Fox Business Network, according to the Times.

The Iranian mission to the United Nations did not immediately respond to a request for comment from the Times. Iran’s foreign minister said in March that Tehran had received “military cooperation” from China and Russia but offered no specifics, the report said.

Since the war began, China has provided Iran with intelligence, access to a spy satellite tracking U.S. forces in the region, and dual-use components, including semiconductors, sensors, and voltage converters used to build drones and missiles. Proving Tehran with finished weapons, however, would mark a significant escalation, and the alleged plan to mask shipments through third countries suggests Beijing wants to keep any such transfers concealed, the newspaper said.