Standing just a few strides from the Syrian border, an Iraqi was mingling with Syrian rebel units outside their camp here, trying to find one that would take him in and let him fight in the uprising.

"It's an honor for me," said Sheik Abu Abdullah, wearing the white robe, Islamic skullcap and beard common among Islamic hardliners.

The battle-hungry Iraqi is part of a stream of Arab fighters who have been drawn to the rebel cause, adding not only to the growing complexities of Syria's civil war but also deepening the uncertainties of what could follow Bashar Assad's regime.

After the latest blow to Damascus — this week's defection of Syria's prime minister — U.S. Secretary of State Hillary Rodham Clinton said Tuesday that there is an urgent need to plan for what happens afterward if and when the Assad regime falls. She said it is important to ensure that Syrian state institutions remain intact. The hope among U.S. officials is to find a "soft landing" that keeps some degree of stability.