Iran has said that it would retaliate against new sanctions imposed by the United States after US President Donald Trump set an ultimatum to fix "disastrous flaws" in a deal curbing Tehran's nuclear programme.

Yesterday, Mr Trump said he would waive nuclear sanctions on Iran for the last time to give the United States and European allies a final chance to amend the pact.

Washington also imposed sanctions on the head of Iran's judiciary and others.

Russia - one of the parties to the Iran pact alongside the United States, China, France, Britain, Germany and the European Union - called Mr Trump's comments "extremely negative".

The ultimatum puts pressure on Europeans, key backers of the 2015 nuclear deal, to satisfy Mr Trump, who wants the pact strengthened with a separate agreement within 120 days.

While approving the waiver on US sanctions related to the nuclear deal, Washington announced other sanctions against 14 Iranian entities and people, including judiciary head Ayatollah Sadeq Larijani, a close ally of Iran's Supreme Leader Ayatollah Ali Khamenei.

Describing sanctions against Mr Larijani as "hostile action", Iran's Foreign Ministry said the move "crossed all red lines of conduct in the international community and is a violation of international law and will surely be answered by a serious reaction of the Islamic Republic," state media reported.

It did not specify what any retaliation might involve.

Iran's Foreign Minister Mohammad Javad Zarif had earlier said on Twitter that the deal was "not renegotiable" and that Mr Trump's move "amounts to desperate attempts to undermine a solid multilateral agreement".

Iran said its nuclear programme has only peaceful aims and said it will stick to the accord as long as others respect it.

But it has said it would "shred" the deal if Washington quit.

Donald Trump has described the 2015 Iran nuclear deal as 'the worst ever'

Mr Trump, who has sharply criticised the deal reached in Barack Obama's presidency, had chafed at having to once again waive sanctions on a country he sees as a threat in the Middle East.

"Despite my strong inclination, I have not yet withdrawn the United States from the Iran nuclear deal," Mr Trump said in a statement, saying the options were to fix "the deals disastrous flaws, or the United States will withdraw."

"This is a last chance," Mr Trump said, pushing for a separate agreement and saying the United States would not waive sanctions again to keep Iran in the pact without such an agreement.

Russian Deputy Foreign Minister Sergei Ryabkov called Mr Trump's remarks "extremely negative", RIA state news agency reported. "Our worst fears are being confirmed," he said.

The EU said in a statement it had taken note of Mr Trump's decision and would assess its implications.

"It's going to be complicated to save the deal after this," said one European diplomat, speaking on condition of anonymity.

On Thursday, Britain, France and Germany had called on Mr Trump to uphold the pact.

Senior US administration officials told reporters that Mr Trump would work with Europeans on a follow-on deal to enshrine triggers that the Iranian government could not exceed related to ballistic missiles.