This image taken from video obtained from Ugarit News, which has been authenticated based on its contents and other AP reporting, shows a rocket fired by Syrian rebels at Mannagh air base in the Aleppo province of Syria on May 13, 2013. (Associated Press/Ugarit News via AP video)
White House press secretary Jay Carney listens to a question from the media during his daily news briefing at the White House in Washington on Monday, May 6, 2013. Carney answered questions about Syria and chemical weapons, as well as Israeli action in Syria. (AP Photo/Jacquelyn Martin)
This citizen journalism image provided by Lens Young Homsi, which has been authenticated based on its contents and other AP reporting, shows buildings which were destroyed from Syrian forces shelling, in Homs province, Syria, Tuesday, May 14, 2013. (AP Photo/Lens Young Homsi)
This citizen journalism image provided by Lens Young Homsi, which has been authenticated based on its contents and other AP reporting, shows buildings which were destroyed from Syrian forces shelling, in Homs province, Syria, Tuesday, May 14, 2013. (AP Photo/Lens Young Homsi)
President Barack Obama gestures during a joint news conference with British Prime Minister David Cameron, Monday, May 13, 2013, in the East Room of the White House in Washington, where they talked about subjects ranging from Syria's civil war to preparations for a coming summit in Northern Ireland. (AP Photo/J. Scott Applewhite)
President Barack Obama gestures during a joint news conference with British Prime Minister David Cameron, Monday, May 13, 2013, in the East Room of the White House in Washington, where they talked about subjects ranging from Syria's civil war to preparations for a coming summit in Northern Ireland. (AP Photo/J. Scott Applewhite)
President Obama gestures during a joint news conference with British Prime Minister David Cameron on Monday, May 13, 2013, in the East Room of the White House in Washington, where they talked about subjects ranging from Syria's civil war to preparations for a coming summit in Northern Ireland. (AP Photo/J. Scott Applewhite)
Pallbearers carry the remains of Fehmi Karaca, 69, a shop owner who was killed in Saturday's explosions, for burial in Reyhanli, near Turkey's border with Syria, on Sunday, May 12, 2013. The bombings marked the biggest incident of cross-border violence since the start of Syria's bloody civil war and have raised fears of Turkey's being pulled deeper into the conflict. (AP Photo/Burhan Ozbilici)
Pallbearers carry the remains of Fehmi Karaca, 69, a shop owner who was killed in Saturday's explosions, for burial in Reyhanli, near Turkey's border with Syria, on Sunday, May 12, 2013. The bombings marked the biggest incident of cross-border violence since the start of Syria's bloody civil war and have raised fears of Turkey's being pulled deeper into the conflict. (AP Photo/Burhan Ozbilici)
