Moscow: Moscow warned on Monday there would be “negative consequences” if US President Donald Trump fails to uphold the landmark Iran nuclear deal negotiated by his predecessor.

Trump is a fierce critic of the 2015 accord, which he has called “the worst deal ever”, and US officials say he intends to tell Congress next week that Tehran is not honouring its side of the bargain.

“Obviously if one country leaves the deal, especially such a key country as the US, then that will have negative consequences,” Russian President Vladimir Putin’s spokesman said.

Putin has repeatedly hailed the importance of the existing deal, he added.

Trump is expected to announce that he is “decertifying” Iran’s compliance with the agreement it signed to limit its nuclear programme in exchange for sanctions relief.

US officials insist this will not sink the deal itself but open the way for Congress to possibly develop new measures to punish other aspects of Iran’s behaviour.

Resumed sanctions could derail the accord negotiated with Tehran by former president Barack Obama and other major world powers.

Congress requires the president to certify Iranian compliance with the deal every 90 days. The next certification date is October 15.

Under the law, Congress would then have 60 days to decide whether to reimpose sanctions lifted by the deal.

Trump is also expected to designate Iran’s most powerful military force, the Revolutionary Guards Corp (IRGC) as a terrorist organisation.

“We are hopeful that the United States does not make this strategic mistake,” Iranian foreign ministry spokesman Bahram Qasemi said.

“If they do, Iran’s reaction would be firm, decisive and crushing and the United States should bear all its consequences,” he added.

Individuals and entities associated with the IRGC are currently on the US list of foreign terrorist organisations, but the organisation as a whole is not.

IRGC commander Mohammad Ali Jafari said on Sunday “if the news is correct about the stupidity of the American government in considering the Revolutionary Guards a terrorist group, then the Revolutionary Guards will consider the American army to be like Daesh all around the world.”