U.S. Secretary of Defense Leon Panetta says he is confident the United States could enforce a no-fly zone over Syria, but that a “major decision” needed to authorize such a mission has not been made.

Panetta told the Associated Press the United States has planned for a number of possible events in Syria. He says a no-fly zone is difficult to implement, and is not a top priority.

Meanwhile, foreign ministers of the Organization of Islamic Cooperation are holding a summit in Mecca Tuesday, after agreeing to recommend suspending Syria from the group.

The move by the 57-member OIC could lead to a diplomatic dispute during the summit between Syrian ally Iran and pro-opposition Saudi Arabia.

Also Tuesday, the United Nations humanitarian chief begins a three-day visit to Syria and Lebanon to discuss ways to urgently boost relief efforts to civilians caught up in the conflict.

In China, the country's foreign minister is scheduled to hold talks with a special envoy to Syrian President Bashar al-Assad. China says it is also considering inviting opposition members to visit.

China has joined Russia in vetoing three United Nations Security Council resolutions threatening Syria with sanctions for using heavy weapons against civilians.

Syrian rebels on Monday circulated video of what they claim is the downing of a Syrian plane and the captured pilot. The rebel video cannot be independently verified.

State media say a pilot ejected Monday after suffering technical problems during a “routine training mission” in eastern Syria, and that authorities are searching for him.