Trump on Tuesday said the United States had agreed to a request by Pakistani mediators "to hold our Attack on the Country of Iran until such time as their leaders and representatives can come up with a unified proposal ... and discussions are concluded, one way or the other."
Pakistan's leaders have hosted peace talks in Islamabad to end a war that has killed thousands of people and shaken the global economy. But even as he announced what appeared to be a unilateral ceasefire extension, Trump also said he would continue the US Navy's blockade of Iran's trade by sea, considered an act of war by Iran.
There was no response early on Wednesday to Trump's announcement from senior Iranian officials, although some initial reactions from Tehran suggested Trump's comments were being treated sceptically.
Trump's wartime rhetoric has veered between extremes. In an expletive-filled threat against Iran only two weeks ago he promised that a "whole civilisation will die tonight", while at other times has appeared keen to end the violence and market uncertainty.
With his announcement, Trump again pulled back at the last moment from his threats to bomb Iran's power plants and bridges.
United Nations Secretary General António Guterres and others have condemned those threats, noting international humanitarian law forbids attacks targeting civilians and civilian infrastructure.
The US and Israel began the war on February 28 with aerial bombardments of Iran. The conflict quickly spread to Gulf states that host US military bases and to Lebanon once the Iran-allied militant group Hezbollah joined the fighting.
Israeli Prime Minister Benjamin Netanyahu has for decades sought to oust Iran's leadership, but Trump has given shifting and sometimes contradictory rationales for joining Israel to launch the war and how he foresees it ending, stirring confusion in global markets.
More than 5000 civilians have been killed across the region and hundreds of thousands displaced so far, mostly in Iran and Lebanon, and the war has led to the virtual closure of the Strait of Hormuz, a vital chokepoint in global energy markets between Iran and Oman, sending oil prices soaring and fears that the global economy could enter a recession.
Iran has repeatedly exploited its ability to control the passage of oil tankers and other ships in the strait in response to US and Israeli attacks.
Before Trump's latest announcement, a senior Iranian official told Reuters that Iran's negotiators had been willing to attend another round of talks if the US abandoned a policy of pressure and threats, and rejected negotiations aimed at surrender.
Iran has condemned the US Navy intercepting and seizing two commercial Iranian ships at sea as part of its blockade, the second earlier on Tuesday, with its foreign ministry accusing the US of "piracy at sea and state terrorism".
The US, joined by multiple other countries, has condemned Iran for impeding freedom of navigation in the Strait of Hormuz.
A first session of talks 10 days ago produced no agreement, with much of the focus on Iran's stockpiles of highly enriched uranium.
Trump wants to take the uranium out of Iran in order to prevent the country from enriching it further to the point where it could develop a nuclear weapon.
Iran says it has only a peaceful civilian nuclear program and a sovereign right to continue that as a signatory of the nuclear weapons non-proliferation treaty.
