Ankara:  The United States and Turkey are reviewing how to help Syria if pro-democracy protests drive President Basher Al Assad from power, US Vice-President Joe Biden said on Sunday, but the two allies have not discussed concrete "next steps".

Washington and Ankara have both called for Al Assad to go, but both worry it could deepen instability in a region already rocked by the Arab Spring, and as US troops leave Iraq by the end of the month.

Biden, in an interview with reporters travelling with him to Athens from Istanbul, said the collapse of the Al Assad regime would not necessarily spark a wider regional sectarian conflict, which some see pitting the Sunni-dominated west of neighbouring Iraq against Shiites in that country and in Iran.

"There was a sense in our discussions that it would be able to be handled without any conflagration going beyond Syria, and that it could be localised to Syria," said Biden, characterising his meeting with Turkish Prime Minister Recep Tayyip Erdogan on Saturday.

Turkey has joined the Arab League in slapping tough sanctions on Syria, once a close friend, in response to Al Assad's bloody crackdown on protests, and has talked openly about the need to be ready for any scenario, including setting up a buffer zone to contain any mass influx of refugees.

France has separately talked about a "humanitarian corridor" to help civilians caught in the violence that has killed over 3,500 people.

Biden, speaking to reporters in his private cabin on Air Force Two, said the issue of a buffer zone had not come up in his two-hour meeting with Erdogan.

"[To] the extent we talked about any ‘what-next' steps, there were generic discussions about having to go in and provide some help and possibly economic assistance and stability, not militarily, but helping the Syrians," Biden said.

"We're in this to see [Al] Assad come down and then determine what would be the most helpful thing for the international community to do to establish stability in that country."

Committed to region

Biden's eight-day trip began in Iraq, and he spent much of his time with Erdogan and Turkish President Abdullah Gul, who he met the day before in Ankara, talking about the country's future after US troops have pulled out. Biden said his main message was to emphasise that although the American war in Iraq was over, the United States remained engaged.

Washington and Ankara have kept in close touch over Syria but differ in their approach to Iran. Washington wants Ankara to adopt tougher sanctions against Tehran, but that is hard for the Turks, who get about 30 per cent of their imported oil from Iran.

Biden said the United States and Turkey might disagree "tactically" about sanctions on Iran, but shared the same strategic goal.