The US and Iran are due to start high-stakes talks in Oman over Tehran's nuclear programme that are being seen as representing one of the last chances to prevent a new US attack.
The negotiations are the first since the US struck Iranian nuclear targets in June, joining in the final stages of a 12-day Israeli bombing campaign.
Washington wants to expand the talks to cover Iran's ballistic missiles, support for armed groups around the region and "treatment of their own people" - as the US secretary of state, Marco Rubio, said on Wednesday - but after days of speculation Iranian negotiators are satisfied that only the nuclear dispute will be discussed, at least initially.
The talks are being held against the backdrop of repeated warnings by Donald Trump that he will strike Iran militarily from the US carrier strike group Abraham Lincoln if no progress is made. The US has been building up its naval presence in the region after a bloody Iranian government crackdown on nationwide protests last month, heightening tensions between Washington and Tehran.
Abbas Araghchi, the Iran foreign minister and a nuclear negotiator with more than 20 years' experience, is pitted against Steve Witkoff, Trump's special envoy, and Jared Kushner, the president's brother-in-law.
Iran is seeking assurances that the US is not using the talks as a smokescreen to impose regime change. The last set of talks between the two sides were brought to a halt in June when Israel launched its surprise attack, which ended with at least 1,000 Iranians dead and three of its nuclear sites destroyed.
Before the talks, Tehran said the US had to drop its request for the negotiations to be held in Turkey in the presence of foreign ministers from Qatar, Turkey, the United Arab Emirates, Egypt and Saudi Arabia.
The planned attendance by the Muslim foreign ministers underlined the extent to which they fear their national security is wrapped up in agreement between the US and Iran.
Tehran has said it will not hesitate to attack Israel or US military bases in the region if it is attacked.
Iran says its right to enrich uranium on Iranian soil - a right it was granted in the now-defunct 2015 nuclear deal negotiated by Barack Obama - is not negotiable. The best source of compromise is that Iran agrees to suspend plans to enrich uranium for a fixed number of years, and a regional consortium is formed that enriches uranium, taking the region closer to an integrated civil nuclear programme.
Iran will also be seeking sanctions relief in return for a new inspections regime at its nuclear sites. The value of the rial against the dollar has halved since the Israeli attacks in June, and Iran's plummeting standard of living, made worse by runaway food inflation close to more than 100%, was the spark for the demonstrations that broke out in late December. The security services responded with a brutal crackdown.
Trump at one point encouraged the protests, promising "help is on its way", but the US held back from attacking Iran partly because Israel and the US military did not feel they were fully prepared to withstand the likely Iranian reprisals.