Tehran and Washington announced Sunday they had agreed a memorandum of understanding aimed at ending the conflict, which broke out on February 28 with US-Israeli strikes on Iran and engulfed the Middle East.

"At this stage, the signing is scheduled for Friday, June 19, at Burgenstock," Switzerland's foreign ministry said in a statement.

The uber-plush resort, perched high above Lake Lucerne in central Switzerland, is difficult to access, with water on three sides, and therefore easily secured.

The location, the ministry said, "was proposed by the Pakistani and Qatari mediators, as well as by the US and Iran".

"Switzerland is acting as a facilitator in this process, creating the practical and diplomatic conditions necessary for this meeting to take place on Swiss territory."

The deal follows weeks of fraught negotiations and threats of renewed hostilities.

According to a senior US official, the framework agreement has already been signed electronically by US President Donald Trump, Vice President JD Vance and Iran's deputy foreign minister, Mohammad Bagher Ghalibaf, the Islamic republic's top negotiator.

The text of the agreement has not been made public, leaving room for doubt over what specifically was agreed in the arduous negotiations to end the conflict.

The sides disagreed bitterly on terms around Iran's nuclear programme, sanctions and the Strait of Hormuz.

But Vance told CNN it was "about a page and a half, so it is a very general document".