Iran and Hezbollah, its Lebanese proxy, are building a network of militias inside Syria to preserve and protect their interests in the event that President Bashar Assad's government falls or is forced to retreat from Damascus, according to U.S. and Middle Eastern officials.
The militias are fighting alongside Syrian government forces to keep Assad in power. But officials believe Iran's long-term goal is to have reliable operatives in place in the event that Syria fractures into separate ethnic and sectarian enclaves.
A senior Obama administration official cited Iranian claims that Tehran was backing as many as 50,000 militiamen in Syria.
"It's a big operation," the official said. "The immediate intention seems to be to support the Syrian regime. But it's important for Iran to have a force in Syria that is reliable and can be counted on."
Iran's strategy, a senior Arab official said, has two tracks.
"One is to support Assad to the hilt, the other is to set the stage for major mischief if he collapses," the official said.
Syrian fragmentation along religious and tribal lines is a growing concern as the civil war approaches its third year with little sign of a political solution or military victory for either Assad's forces or the rebels.
Rebel forces, drawn largely from Syria's Sunni majority, are far from united, with schisms along religious, geographic, political and economic lines.
Militant Islamists, including many from other countries and with ties to al-Qaida, are growing in power.
"Syria is basically disintegrating as a nation, similar to how Lebanon disintegrated in the '70s to ethnic components, and as Iraq did," said Paul Salem, director of the Beirut-based Mideast Center of the Carnegie Endowment for International Peace.
"It's going to be very hard to put Syria the nation back together," Salem said.
Experts said that Iran is less interested in preserving Assad in power than in maintaining levers of power, including transport hubs inside Syria.
As long as Tehran could maintain control of an airport or seaport, they could maintain a Hezbollah-controlled supply route into Lebanon and continue to manipulate Lebanese politics.