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.
"Our intelligence services and our military have very important responsibilities and roles to play, so we are going to be setting up a working group to do exactly that," she added. "We have planned for many contingencies, including the very horrible scenario of the use of chemical weapons." 
Asked if such discussions included options such as imposing a no-fly
zone over territory that Syrian rebels claim to control, Clinton
indicated that was a possible option.
"The issues you posed within your question are exactly the ones the minister and I agreed need greater in-depth analysis," Clinton answered, although she indicated no decisions were necessarily imminent.
In Washington, the Treasury and State departments announced new sanctions on Syria's state-run oil company
Sytrol, saying it had supplied gasoline to Iran, and on Lebanon-based Hezbollah, charging that the group had provided training, advice and extensive logistical support to Assad's government.
The
sanctions will add to Washington's arsenal of economic measures targeting both Syrian organizations and foreign entities, mostly in Iran, accused of helping Assad's government. While imposing economic pain on Damascus, the sanctions have not halted Assad's bloody crackdown on his opponents.
Rebels fighting Assad's forces in
Aleppo said they were preparing a new attack on Friday after having been pushed back by government units seeking to reestablish control over Syria's largest city and its economic hub.
US officials say Clinton's one-day stop in Istanbul will give the United States and its NATO partner Turkey a chance to compare notes on Syria following a string of dramatic swings in Assad's push to crush an armed rebellion.
Washington sees
Turkey, one of Damascus' harshest critics, as the key player both in supporting Syria's opposition and in planning for what US officials say is the inevitable collapse of the Assad government following some 17 months of bloodshed.
US officials are particularly interested in Turkey's analysis of the political forces emerging as Syria spirals into chaos - hoping that together they can puzzle out the complex patchwork of rebel groups jockeying for position. Clinton is due to meet a range of Syrian opposition figures in Turkey, but not members of armed fighting groups.
.
The US official said Clinton's talks in Turkey would focus on the non-lethal aid that the United States is already providing, but would also look at unspecified additional measures that it might take to be more effective.
Turkey this week accused Assad of
supplying arms to Turkish Kurd militants, and Prime Minister Tayyip Erdogan has raised the possibility of military intervention in Syria if the Kurdish threat increases.
US officials have commented that Clinton will also announce additional US humanitarian aid and plan with Turkey on how to handle the refugee crisis created by Syria's violence.
Turkey has received more than
50,000 refugees from Syria, and the United Nations estimates that approximately 2 million people in Syria are in need of humanitarian assistance, and more than 140,000 people have fled to neighboring countries that also include Jordan, Lebanon, and Iraq.