US Secretary of State Hillary Clinton has arrived in Turkey for crisis talks on the civil war in Syria.
During the next few days, she will meet Prime Minister Recep Tayyip Erdogan to discuss US support for rebels fighting Bashar al Assad’s regime.
They will also discuss ways to enforce sanctions against Syria and support for Turkey’s hosting 50,000 Syrian refugees stranded in camps along the country’s border.
Turkey is traditionally a close ally of Syria but has become a vocal opponent of the regime since Mr Assad launched a fierce response to the uprising in March 2011.
Relations between the two countries reached a low after a Turkish fighter jet was shot down by Syrian fire in June, killing its two-man crew.
A US official said: “The Secretary was very clear that we don’t want to put a date on Assad’s departure, because we don’t know when that day will come.
“But it is our strong conviction that it will come and the international community needs to be prepared to support the Syrians as they deal with the challenges that will come with effectuating transition to a new Syria.”
Mrs Clinton is also expected to announce a further $5.5m (£3.5m) in aid for refugees who have fled the fighting.
Direct US support for the rebels is partly a result of the United Nations Security Council being divided on the Syrian issue. Russia and China have blocked the last three draft resolutions.
“We made clear we were shifting from New York to a focus on supporting the opposition… and to begin in earnest planning for the day after Assad falls,” the US State Department official said.
“There are political challenges in terms of organising the state and protecting its institutions.
“There are economic challenges, both in terms of short-term stabilisation and in terms of rebuilding a deteriorating Syrian economy.
“There are (also) security challenges that may require international and multilateral assistance of various kinds.”
Washington recently announced sanctions against Syrian state oil company Sytrol for trading with Iran, to punish both regimes and starve them of much-needed revenue.
Reporting from the Syrian-Turkish border, “The last 10,000 refugees have arrived in the last week now that the fighting has moved to Aleppo and become very nasty indeed.
“We were in the towns and villages just north of Aleppo where a lot of people have moved, thinking they would be safe.
“But now the air strikes are targeting those areas as they believe the Free Syrian Army and opposition rebels are based there and supplying fighters and munitions into Aleppo.
“So the whole area is dangerous now which means more people will be pushing themselves towards Turkey.”