MOSCOW - Iran said on Saturday it would retaliate against new sanctions imposed by the United States after President Donald Trump set an ultimatum to fix "disastrous flaws" in a deal curbing Tehran's nuclear program.Trump said on Friday 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 Trump's comments "extremely negative."The ultimatum puts pressure on Europeans, key backers of the 2015 nuclear deal, to satisfy 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 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 Trump's move "amounts to desperate attempts to undermine a solid multilateral agreement."Iran says its nuclear program has only peaceful aims and says it will stick to the accord as long as others respect it. But it has said it would "shred" the deal if Washington quit.