US President Donald Trump's decision to withdraw from the 2015 agreement constitutes "a complete disregard for international law and the United Nations Charter", Mohammad Javad Zarif said in the letter.

His actions "undermine the principle of peaceful settlement of disputes, endanger multilateralism and its institutions, indicate a regress to the failed and disastrous era of unilateralism, and encourage intransigence and illegality," he added.

The letter was written to UN Secretary General Antonio Guterres on May 10, two days after Trump made the historic move to pull out of the agreement and reimpose sanctions on Iran.

It was only published Monday on the website of the Iranian foreign ministry.

Zarif is on a diplomatic tour of China, Russia and Europe, the other backers of the agreement who strongly opposed Trump's decision and hope to salvage the deal.

Unlike Iran, "which has scrupulously fulfilled its undertakings... the United States has consistently failed -- since 'implementation day', and particularly after the assumption of office by President Trump -- to abide by its commitments," Zarif wrote in the letter.

He said Trump's withdrawal also meant multiple cases of "significant non-performance" with the nuclear deal, and "clear non-compliance" with resolution 2231 of the UN Security Council, which endorsed the deal.