Beijing said on Monday that there can be no winners in a tariff war, after a spokesman was asked to comment on US President Donald Trump's threat to impose a 50 percent tariff on China if it supplies weapons to Iran.

Foreign Ministry spokesman Guo Jiakun told a regular news briefing that China's position on the issue is very clear.

In response to reports that China is preparing to deliver new air defense systems to Iran, Guo said China has always adopted a prudent and responsible approach to military exports.

He said China exercises strict control in accordance with its export control laws and regulations and the international obligations it has undertaken.

China opposes groundless smears and malicious attempts to draw connections, he added.