The UN began efforts to evacuate hundreds of ships from the Gulf in a tentative return to calm after a fragile peace deal Tuesday.
For his part, US President Donald Trump said Iran had agreed to nuclear inspections into "infinity," despite Tehran's denials.
The UN shipping agency said an evacuation plan to enable some 11,000 seafarers stuck aboard vessels in the Gulf to sail through the Strait of Hormuz, which Iran effectively blocked during the war, was underway after the ceasefire deal between Washington and Tehran.
Speaking at the United Nations, spokesman Stephane Dujarric expressed relief for the stranded.
"The operation marks a significant step towards alleviating the humanitarian impact of the crisis on thousands of seafarers who have endured months of uncertainty," he said.
IMO Secretary-General Arsenio Dominguez said the "large-scale operation" would unfold in close cooperation with Iran, Oman, other coastal states, the US and the maritime industry.
In another sign of de-escalation, Washington agreed to waive sanctions on Iran for 60 days from Monday after the first round of talks under the nascent peace deal agreed last week on ending more than three months of war. Trump also said unfrozen Iranian assets would be used to buy humanitarian supplies from the US
