WASHINGTON -- The bloodshed in Syria has continued for so long that extremist forces have taken charge, with U.S. officials saying they now face two familiar enemies in the struggle to find a resolution: al Qaida in Iraq cells and Iranian-backed sectarian militias.

Those groups were responsible for thousands of American and Iraqi casualties during the eight years U.S. forces fought them next door in Iraq. Now, U.S. officials and some analysts say, the Sunni Muslim extremists of al Qaida have regrouped in Syria as the Nusra Front, the leading rebel faction fighting President Bashar Assad’s regime. The Syrian military, meanwhile, is relying increasingly on backup from the thuggish pro-Assad militias known as shabiha, elements of which receive Iranian training and funding, U.S. officials say.

“Round 2,” said Joe Holliday, a Washington-based researcher who specializes in Syrian militants at the Institute for the Study of War, noting the resurgence of two foes the United States thought it had left behind after withdrawing from Iraq last year.

The Obama administration designated the Nusra Front and elements of the shabiha as terrorist groups earlier this month in a move to isolate extremists on the battlefield. While few observers dispute that al Qaida-style forces have moved into Syria from Iraq, some analysts say the U.S. government might be overstating the Iranian role with the shabiha, an unstructured entity that was born of Syrian clan loyalty rather than any shared ideology with the Iranians. However, the analysts added, the chance for more Iranian involvement only increases as the bloodshed nears its second year with no end in sight.

With unfriendly forces now on both sides of the conflict, analysts say, the U.S. seems out of policy options in Washington as its leverage on the ground in Syria evaporates. Joshua Landis, a Syria expert who’s the director of the Center for Middle Eastern Studies at the University of Oklahoma, said the Obama administration was now sandwiched between its archenemies al Qaida and Iran, making it hard to maintain a position of avoiding direct involvement in the conflict.

“America is paralyzed,” Landis said. “They don’t like Assad, but they’re even more fearful of the rebels.”

The Nusra Front’s connections to Iraq seem concrete, with U.S. officials tracking movement of the group’s leaders from the northern Iraqi city of Mosul to Syria in late 2011. The administration believes that Nusra is just a renamed incarnation of Iraq’s al Qaida branch, which has “dispatched money, people and materiel from Iraq to Syria over the past year,” one senior administration official said, speaking only on the condition of anonymity in a conference call this month. Nusra fighters have openly – and proudly – admitted that they’re veterans of the anti-U.S. insurgency in Iraq.

The Syrian regime’s connections to Iran and the Iranian-backed Shiite Muslim militias based in Iraq are harder to prove, analysts say, though that hasn’t stopped the Obama administration from drawing direct links. During the conference call this month, a second senior administration official said the Syrian shabiha known as Jaysh al Shaabi, or the People’s Army, was modeled after the powerful Iranian paramilitary group known as the Basij.

“Jaysh al Shaabi was created and continues to be funded and maintained with support from Iran and Hezbollah, and it is modeled after the Iranian Basij militia, which has proven so deadly and effective at using violence and intimidation to suppress political dissent in Iraq,” the official said.