The lightning overthrow of President Bashar Assad left Syrians, countries in the region and world powers nervous on Tuesday about what comes next as the rebel alliance took its first steps in a government transition.

The United Nations Security Council met behind closed doors late Monday, and diplomats said they were still in shock at how quickly Assad's overthrow unfolded over 12 days, after a 13-year civil war that was locked in stalemate for years.

"Everyone was taken by surprise, everyone, including the members of the council. So we have to wait and see and watch ... and evaluate how the situation will develop," Russian U.N. Ambassador Vassily Nebenzia told reporters after the body met.