"We have always believed that there are no winners in a tariff war, and China will resolutely safeguard its legitimate rights and interests," foreign ministry spokeswoman Mao Ning told a regular news conference when asked about Trump's levy announcement.

A rights group has estimated that a violent crackdown on protests has killed at least 648 people in Iran as authorities sought to regain control of the streets with mass nationwide rallies.

In response to a question about advice for Chinese citizens travelling to Iran for tourism, Mao said Beijing was "closely monitoring the development of the situation".

"We will take all necessary measures to protect the safety of Chinese citizens," she said.