A Syrian man looks at the rubble of a five story apartment building that was destroyed in a barrel bomb attack in the al-Shaar neighbourhood of the northern city of Aleppo on August 27, 2014. Syrian war planes carried out a series of air raids on positions held by the Islamic State jihadist group in eastern Deir Ezzor province, an NGO and state media said. AFP PHOTO / ZEIN AL-RIFAI / AMC (Photo credit should read ZEIN AL-RIFAI/AFP/Getty Images)

WASHINGTON -- As President Barack Obama weighs airstrikes in Syria against the Islamic State (ISIS), he may soon have to grapple with the possibility that a successful mission against the extremist group could require collaboration with Syrian President Bashar Assad.

The Obama administration has flatly ruled out working alongside the same regime that has committed large-scale atrocities during the Syrian civil war. But several military and counterterrorism analysts believe the U.S. may be left with limited options should it go after ISIS in the region absent a tacit agreement, at the very least, with Assad.

Unilateral action, some argue, would expose the U.S. to a number of risks -- be it the downing of one of its military aircraft or gaps in intelligence that would make a successful bombing campaign against ISIS difficult to execute.

“Probably the greater risk is that there's an unintentional hit. I don't think it's outside the realm of possibility that they would target U.S. aircraft,” said Ken Sofer, an associate director for national security and international policy at the Center for American Progress. “The Assad regime is very worried that even if the U.S.' main target in Syria is ISIS, would the U.S. do a double strike against the Assad regime and ISIS?"

Seizing on an opportunity to legitimize his government, Assad has said he is open to partnering with the U.S. against ISIS and warned the Obama administration against acting unilaterally.

Karl P. Mueller, a senior political scientist with the RAND Corporation, said that while the U.S. could have some success acting on its own against ISIS, there are a few reasons why the government might want to take Assad up on his offer.

“It reduces the chance of an aircraft getting shot down, depending on where the ISIS targets are,” Mueller said, pointing out that surface-to-air missiles would be of greater concern if targets are close to the Syrian front lines. “You also conceivably could want to coordinate, because Assad has intelligence that would be useful to you in terms of location of the targets.”

Mueller added that the U.S. has worked with its adversaries before, such as cooperating with the Soviet Union during World War II or with China in the latter part of the Cold War. The case the administration could make if it were to coordinate with Assad, he said, would be to place the focus on eliminating ISIS while achieving some sort of settlement in the Syrian civil war.

The White House, for its part, appears to be inching closer to military action in Syria, with Obama authorizing surveillance flights in the region. But State Department spokeswoman Jen Psaki told reporters last week that coordination of any kind with Assad is not on the table.

“We’re not going to ask for permission from the Syrian regime,” Psaki said.

Joshua Landis, director of the Center for Middle East Studies and associate professor at the University of Oklahoma, cautioned that such declarations might be premature.

“The problem with making those kinds of statements and washing your hands of Assad is that if you sit down with the authorities in Baghdad and you show them what your drones that have been flying over Syria tell you about ISIS, chances are that somebody in that room, some Iraqi in that room, is going to call up Bashar al-Assad within minutes after the Americans leave and say 'here's where the concentration of ISIS are, go bomb them.' And Assad will.”

“Now that's not America coordinating with Syria, but it sort of is,” he added.

Stephen Biddle, an adjunct senior fellow for defense policy at the Council on Foreign Relations and an international affairs professor at George Washington University, argued that airstrikes could still be carried out without conveying any legitimacy to the Assad regime. “It’s not as though we’re improving his status and stature in the international political system at the same time,” he said.

Biddle echoed concerns that Assad’s forces could shoot at U.S. aircraft if there is no understanding between the two sides, but referred to Israel as an example of another government that has gone after targets in Syria and “lived to tell the tale.”

It would not be in Assad’s interest, he added, to really discourage the U.S. from striking a shared enemy. Taking action against ISIS would “at some level improve Assad’s probability of survival," other things being held constant, he said.

Shadi Hamid, a fellow at the Brookings Institution's Center for Middle East Policy, also deemed it unlikely that the Syrian regime would go after U.S. forces in Syrian airspace.

“The last thing that the regime wants to do is actually provoke the U.S. into a confrontation,” said Hamid, who recently authored Temptations of Power, a book on Islamist movements. “Anything that undermines ISIS' position is going to by definition benefit Assad's regime. If you just kind of look at it from that zero-sum perspective, there would definitely be a convergence of interest there.”

The bigger question, Hamid said, is whether airstrikes would be accompanied with a broader strategy to strengthen the position of mainstream rebels who have exhausted many of their resources fighting both ISIS and the Assad regime with little support from the United States and international community. The U.S. has armed moderate Syrian rebels over the last year, but has been reluctant to provide greater military support, citing concerns over militant groups in the region.

“There's very little to suggest so far that we're serious about supporting mainstream rebel forces in Syria,” Hamid said. “Even if we say we have no plans to coordinate with the Assad regime, we are in effect acting as Assad's air force if we strike ISIS without boosting the other rebels.”