China on Monday called reports it had supplied or intended to supply weapons to Iran "baseless smears," after several outlets quoted US intelligence sources to that effect.
On Sunday, US President Donald Trump threatened Beijing with a "staggering" new tariff of 50 per cent if it were to provide military assistance to Tehran.
His comments came the same day US outlet CNN reported that US intelligence indicated China was preparing to deliver new air defence systems to Iran within the next few weeks, citing three people familiar with the assessments.
Over the weekend, The New York Times quoted US officials as saying US intelligence suggested Beijing might have already sent a shipment of shoulder-fired missiles.
China denied the reports, saying Monday it had "always adopted a cautious and responsible attitude towards the export of military items, implementing strict controls in accordance with its own export control laws and regulations and its international obligations."
"We oppose baseless smears or malicious association," foreign ministry spokesman Guo Jiakun told a regular news briefing.
China is a key economic partner of Iran -- it buys most of the Middle Eastern country's oil.
The countries have no formal military pact, though, and many analysts say Beijing largely sees the relationship between the two as transactional.
China also has strong economic ties to the Gulf countries and has criticised Iran's attacks on them over the course of the war.