US secretary of state meets with Turkish leaders, Syrian opposition on Syria; says Turkey, US "planned for all possible contingencies"; talks follow new sanctions on Syria's state oil company.

US Secretary of State Hillary Clinton landed in Turkey on Saturday morning for meetings with Turkish representatives as both countries plan for Syrian President Bashar Assad's fall.

Clinton, winding up an 11-day Africa tour, flew from the small West African state of Benin to Istanbul, where she plans to meet with Turkey's prime minister and foreign minister and hold talks with Syrians who have recently joined the growing exodus of refugees fleeing the violence.

In a joint press conference with Turkish Foreign Minister Ahmet Davutoglu in Istanbul on Saturday afternoon, Clinton told the press: "We have undertaken very intensive operational planning."

"We have been closely coordinating over the course of this conflict. But now we need to get into the real details of such operational planning and it needs to be across both of our governments," Clinton told reporters in Istanbul.