US Secretary of State John Kerry said Saturday that Syrian President Bashar al-Assad must step down, but not necessarily immediately upon reaching a settlement to end the country's civil war.
Speaking after talks in London with British Foreign Secretary Philip Hammond, Kerry said he was prepared to negotiate to achieve a solution but asked whether Assad was.
"For the last year and a half we have said that Assad has to go but how long, what the modality is... it doesn't have to be on day one or month one or whatever," Kerry told reporters.
"There's a process by which all the parties have to come together and reach an understanding of how this can be achieved."
"We need to get to the negotiation.
That's what we are looking for and we hope Russia, Iran and other countries with influence will help to bring about that because that is what's preventing this crisis from ending," he added.
Russia and the United States launched military talks on the Syrian conflict on Friday as Moscow increased its build-up of forces in the war-torn country.