The contradictory statements suggest there is little prospect for a diplomatic resolution to the war anytime soon.
"They are going on right now," Trump told reporters at an Oval Office event when asked about the state of negotiations, saying the sides were talking at the request of Iran, Saudi Arabia, the United Arab Emirates and Qatar, among others.
"This is a last chance for them (Iran) to sign a good document," he said.
Trump's comments followed his decision this weekend to call off what he said would be "massive attacks" he had authorised on Iran, saying talks were to be held, repeating a pattern in which he has vowed major strikes only to cancel them.
Earlier on Monday, Iranian Foreign Ministry spokesman Esmail Baghaei said no negotiations with the United States were taking place and no meetings were scheduled.
Iran had no plans to host foreign delegations or send negotiators abroad in the coming days, he said.
Gulf officials and analysts say Iran is betting it can outlast Washington by turning the Middle East's trade routes, shipping lanes and energy infrastructure into pressure points that steadily raise the cost of confrontation, hoping to convince the US and its allies that containing the crisis is more costly than accommodating Iran's demands over the Strait of Hormuz.
In a post on Truth Social later on Monday, Trump called Iran's leadership "unbelievably duplicitous," saying they had asked for a meeting and more talks were scheduled for the "immediate future".
He also repeated his assertion that the US Navy had total control over the Strait of Hormuz, through which one-fifth of global oil and liquefied natural gas flowed before the conflict.
"'The United States Wall of Steel!' Nothing gets through to Iran, unless we want it to, and nothing will get through, unless a Deal, or Total Surrender, is accomplished," he wrote.
Monday's developments appeared to fit a pattern that has emerged since Trump launched Operation Epic Fury alongside Israel more than five months ago. On several occasions, Trump has threatened military action only to later cite diplomatic contacts as a reason for stepping back.
Iran, however, has publicly rejected negotiations with Washington since a June memorandum of understanding aimed at ending the conflict collapsed in early July.
Trump has yet to achieve the objectives he set out at the outset of the war: dismantling Iran's nuclear program, curbing its ability to attack regional rivals and creating conditions for Iranians to overthrow their clerical rulers.
Repeated US escalations have been met by escalating Iranian responses against US forces in the region, Washington's Gulf Arab allies and shipping, each time ending with Trump stepping back.
The dispute over the Strait of Hormuz remains a central point of contention. Washington says the June memorandum required Iran to open the strategically vital waterway, while Tehran argues the text explicitly preserved its authority over shipping traffic.
That would leave Tehran with greater leverage over the strait than before the war, a result that would likely be seen as a significant setback for Trump.
So far the US has failed to compel Iran to relinquish its grip on the waterway, sending global oil prices higher and pushing up politically sensitive gasoline prices in the US.
with AP and DPA
