Europe and Iran are to put on a united front in support of the landmark 2015 nuclear deal at talks in Brussels Thursday as Washington mulls reimposing sanctions on Tehran.
The European Union and the foreign ministers of Britain, Germany and France will unite to defend the accord, which curbed Iran's nuclear ambitions in return for the relaxing of punishing sanctions but which US President Donald Trump has repeatedly criticised and threatened to leave.
While EU diplomatic chief Federica Mogherini wants to keep the nuclear issue separate from other contentious issues with Tehran, Iranian Foreign Minister Mohammad Javad Zarif will also face tough questions about recent anti-government protests which left 21 people dead.
Trump, who in October refused to certify Iran was complying with the deal but stopped short of withdrawing from it, is expected to decide on Friday whether to extend waivers on nuclear-related sanctions against Tehran.
The EU and other world powers have repeatedly warned it would be a mistake to abandon the deal, thrashed out with Iran over 12 years by the US, Britain, France, China, Germany and Russia.
British foreign minister Boris Johnson called the deal "a crucial agreement that makes the world safer".
"It is vital that we continue to work with our European partners to preserve the Iran deal, and with it the security and prosperity it is bringing to the people of Iran and the world," he said.
- Iran warning -
According to two US sources, Trump had not made a decision by Wednesday, while Johnson told the British parliament on Tuesday that London was urging "our friends in the White House not to throw it away".
Iran, which on Monday warned the world to get ready for Washington abandoning the deal, has said if the US walks away from the agreement it is ready to give an "appropriate and heavy response".
Zarif, who travelled to Moscow on Wednesday to seek Russian support, criticised what he called Washington's "destructive policy".