China on Tuesday urged parties related to the Iranian nuclear issue to exercise restraint and avoid escalation of tension, after Tehran announced that it had surpassed the limit of the low-grade enriched uranium stockpile under the 2015 Iran nuclear deal, which Washington abandoned.

"China regrets the measures taken by Iran, and as China has repeatedly stressed, the maximum pressure campaign by the US is the root cause of the current Iranian nuclear tension," Chinese Foreign Ministry spokesperson Geng Shuang made this remark at a daily press briefing. 

Iranian Foreign Minister Mohammad Javad Zarif told semi-official news agency ISNA that "Iran has crossed the 300-kilogram limit based on its plan" announced in May. But he also said the move could be reversed.

US President Donald Trump warned Monday that Iran is "playing with fire" after Tehran's announcement.

"They know what they're doing. They know what they're playing with and I think they're playing with fire," Trump told reporters at the White House when asked about Iran.

"The parties to the Iranian nuclear deal have made unremitting efforts to safeguard the pact. At the meeting of the Joint Commission on nuclear deal on June 28, the parties reaffirmed their commitment to the full and effective implementation of the Agreement, and Iran has always stressed its willingness to remain in the pact, and the measures it has taken are reversible," Geng said.

"We call on all parties to bear in mind the overall and long-term interests, exercise restraint, jointly uphold the deal and avoid escalation of tension."

The US withdrew from the nuclear deal last year and hit Iran's crucial oil exports and financial transactions as well as other sectors with biting sanctions.

Tehran, which has sought to pressure the remaining parties to save the deal, announced on May 8 it would no longer respect the limit set on its enriched uranium and heavy water stockpiles.

It threatened to abandon further nuclear commitments unless the remaining partners helped it circumvent sanctions, especially to sell its oil.

The White House had earlier said "the United States and its allies will never allow Iran to develop nuclear weapons," vowing to continue exerting "maximum pressure" on the regime.

"It was a mistake under the Iran nuclear deal to allow Iran to enrich uranium at any level," spokeswoman Stephanie Grisham said in a statement.

The statement added that "even before the deal's existence, Iran was violating its terms," to which Zarif reacted on Tuesday by tweeting "seriously?"

Zarif insisted Iran had done nothing wrong. "We have NOT violated the #JCPOA," he tweeted, referring to the deal.

He said Iran would "reverse" its decision "as soon as E3 abide by their obligations" - referring to the European parties to the deal: Britain, France and Germany.