US and Iranian officials are due to meet in Geneva on Thursday for a third round of indirect talks, as President Donald Trump threatens to strike Iran if a nuclear deal is not reached.
The discussions come amid the largest US military build-up in the Middle East since the US-led invasion of Iraq in 2003, and with Iran vowing to respond to an attack with force.
The talks are seen as a last-ditch effort to prevent a conflict, but the chances of an agreement remain unclear.
While Trump has said he prefers to solve the crisis through diplomacy, he has also said he is considering a limited strike on Iran to pressure its leaders to accept a deal.
The president, however, has done little to explain what he is demanding in the negotiations and why there could be the need to take military action now, eight months after the US bombed Iranian nuclear facilities during a war between Israel and Iran.
Iran has rejected the US demand to stop the enrichment of uranium in its territory, but there have been indications that it is prepared to offer some concessions about its nuclear programme.
