Washington DC - President Donald Trump claimed Monday the US and Iran had held "very good" talks about ending his disastrous war, putting threatened US attacks on Iran's power plants on hold in a stunning U-turn.

In a social media post that immediately sent oil prices tumbling, Trump mentioned "productive conversations" over the last two days towards "a complete and total resolution" of hostilities in the Middle East.

But Iran's foreign ministry reportedly denied any contact and suggested it was all a tactic to bring down energy prices sent soaring by the war.

Trump also claimed he had told the Pentagon to "postpone any and all military strikes against Iranian power plants and energy infrastructure for a five day period, subject to the success of the ongoing meetings."

He insisted the US-Iranian sides would keep talking "throughout the week."

The bombshell announcement came ahead of a Monday night ultimatum for the Islamic republic to reopen the Strait of Hormuz shipping lane, or have its power plants destroyed by the US.

In response, Iran had threatened to deploy naval mines in the Gulf and directly target energy infrastructure across the region.

Tehran has retaliated against US-Israeli attacks by throttling traffic through Hormuz, conduit for a fifth of global crude, hitting energy sites and US embassies across the Gulf as well as targets in Israel.

Throughout the war, Trump and his administration have issued confused and contradictory messages on the motivation, goals, and progress of the war.