Washington stuck to its demand yesterday that Syrian President Bashar al-Assad leave power, ahead of peace talks which will include Assad’s main ally Iran for the first time, reflecting his stronger position since Russia joined the war on his side.

Throughout four years of war that has killed 250,000 people and driven more than 10 million from their homes, Mr Assad’s main ally Tehran was locked out of a succession of international peace conferences, all of which ended in failure.

But four weeks after Russia began bombing Assad’s enemies on the ground, the countries that demand he leave office, including the United States, European powers and Saudi Arabia, have agreed to give Iran a seat at the negotiating table.

“Those who tried to resolve the Syrian crisis have come to the conclusion that without Iran being present, there is no way to reach a reasonable solution to the crisis,” Iran’s Foreign Minister Mohammad Javad Zarif said on his arrival in Vienna yesterday ahead of today’s conference.

US and its European and Middle Eastern allies demand Assad leaves power as part of any peace deal

Mr Zarif met US Secretary of State John Kerry yesterday in Vienna for talks on other issues including the July nuclear agreement between Iran and global powers. Kerry also met Russia’s Sergei Lavrov and the foreign ministers of Saudi Arabia and Turkey.

State Department counsellor Tom Shannon said Mr Kerry would use the conference to see if Tehran and Moscow were willing to accept a change of leadership in Damascus, and gauge their commitment to fighting the Islamic State group. Mr Kerry would assess the extent to which Iran and Russia “are prepared to work broadly with the international community to convince Mr Assad that during a political transition process he will have to go,” Mr Shannon said.

The US and its European and Middle Eastern allies have demanded Assad agree to leave power as part of any peace deal. He refuses to go, and Russia and Iran have consistently rejected any such demands.