"Hopefully Iran will quickly 'Come to the Table' and negotiate a fair and equitable deal - NO NUCLEAR WEAPONS - one that is good for all parties. Time is running out, it is truly of the essence!" Trump wrote in a social media post.
The Republican US president, who pulled out of world powers' 2015 nuclear deal with Tehran during his first White House term, noted that his last warning to Iran was followed by a military strike in June.
"The next attack will be far worse! Don't make that happen again," Trump wrote. He also repeated that a US "armada" was heading toward the Islamic Republic.
Iran's mission to the United Nations responded in kind.
"Last time the US blundered into wars in Afghanistan and Iraq, it squandered over $US7 trillion ($A10 trillion) and lost more than 7000 American lives," it said in an X post quoting Trump's statement.
"Iran stands ready for dialogue based on mutual respect and interests—BUT IF PUSHED, IT WILL DEFEND ITSELF AND RESPOND LIKE NEVER BEFORE!"
Iranian Foreign Minister Abbas Araqchi said he had not been in contact with US special envoy Steve Witkoff in recent days or requested negotiations, state media reported on Wednesday.
Trump said a US naval force headed by the aircraft carrier USS Abraham Lincoln was approaching Iran. Two US officials told Reuters on Monday that the Lincoln and supporting warships had arrived in the Middle East.
The warships started moving from the Asia-Pacific region last week as US-Iranian tensions soared following a bloody crackdown on protests across Iran by its clerical authorities in recent weeks.
Trump has repeatedly threatened to intervene if Iran continued to kill protesters, but the countrywide demonstrations over economic privations and political repression have since abated.
He has said the United States would act if Tehran resumed its nuclear program after the June air strikes by Israeli and US forces on key nuclear installations.
