Beijing rejected on Monday "groundless" reports that Chinese entities supplied Tehran with satellite images of a military base housing US troops in Jordan, before and after an Iranian strike killed three American soldiers.

The reports by the Wall Street Journal over the weekend related to July 17 missile strikes launched by Iran on the Muwaffaq Salti Air Base in Jordan.

Unnamed American officials cited in the Journal's reporting did not name the Chinese entities involved, and did not suggest that Beijing was directly to blame.

"We firmly oppose groundless suspicion and accusations without evidence," Chinese foreign ministry spokesperson Guo Jiakun told a regular news conference on Monday.

US President Donald Trump sought to downplay the reports, which could deepen tensions ahead of a planned visit by Chinese leader Xi Jinping to the White House on September 24.

"You know, when they say that China spies on us, I say you're right, and we spy on them too," Trump told reporters aboard Air Force One on Sunday.

"That's what we do. They basically do what we do," he said. 

Chinese officials asked for proof of the transfer of satellite imagery when prodded by the US officials, and refused to acknowledge that Chinese companies were involved in providing Tehran with satellite images, the Journal reported late Friday.

Trump has warned Beijing not to sell weapons to Iran, and in May, Washington sanctioned three China-based satellite companies for enabling Iran's military operations.

China is a top economic partner of Iran, buying much of its oil output, and also an important diplomatic backer.

Still, Trump said of Xi on Sunday that "he's behaved reasonably well, and we behave reasonably well."

Asked if he would ever allow Chinese cars to be sold in the United States, Trump said "I haven't. I'm the one that kept them out. The tariffs kept them out."