Dozens of U.S. officials have called on the Obama administration to order "targeted military strikes" against the regime of Bashar al-Assad in Syria, with the aim of pressuring Damascus to accept a binding cease-fire and engage in peace talks. 

The Wall Street Journal reported that 51 State Department officials advising Syria policy signed the so-called "dissent channel cable".

State Department spokesman John Kirby confirmed the cable's existence Thursday, but said he would not comment further until officials have reviewed its contents. 

The cable expresses clear frustration with America's inability to halt a civil war that has killed perhaps a half-million people and contributed to a worldwide refugee crisis, and goes to the heart of Obama's reluctance to enter the fray.

"It’s embarrassing for the administration to have so many rank-and-file members break on Syria," a former State Department official told the Journal.

Obama called for regime change early on in the conflict and threatened military strikes against Syrian forces after blaming President Bashar Assad for using chemical weapons in 2013. But Obama only has authorized strikes against the Islamic State (ISIS) and other U.S.-designated terror groups in Syria.

While Washington has provided military assistance to some anti-Assad rebels, it has favored diplomacy over armed intervention as a means of ushering Syria's leader out of power. A series of partial cease-fires in recent months have only made the war slightly less deadly, and offered little hope of a peace settlement.

The U.S. does have military assets available in the region, including two aircraft carriers in the Mediterranean Sea and a number of Air Force jets based at Incirlik Air Force Base in Turkey. 

However, Assad has enjoyed the protection of his Russian allies in recent months, and any action against the Syrian regime would likely bring U.S. and Russian forces into direct conflict. 

Moscow has deployed an advanced S-400 surface-to-air missile system to Syria, as well as dozens of air-to-air interceptors and strike fighters such as the Su-35 and Su-24.

Navy Vice-Admiral James Foggo III, commander of the U.S. Sixth Fleet, told Fox News Thursday that Russia also has two Kilo-class submarines in the Black Sea armed with state-of-the art Kalibr cruise missiles. One kilo boat launched one of these cruise missiles into Syria from the Mediterranean Sea this past December.

Since September, Russia has deployed dozens of jets and helicopter gunships to Syria, which are now spread out among four bases. Russia also has dispatched bombers on missions from Engels and Mozdok, in southern Russia, which have launched cruise missiles and dozens of unguided bombs in the last year. 

Republican and even some Democratic lawmakers have been urging Obama to take greater military action in Syria for years, from air strikes to the establishment of a no-fly zone over rebel-held areas. As secretary of state, Hillary Clinton pushed some of these steps, too.

But Obama has resisted, fearful of leading America into another war in the Muslim world after finding it impossible to withdraw U.S. forces from Afghanistan and keep forces out of Iraq. Military commanders have been similarly reticent, given the lack of a clear alternative to Assad that might unify Syria and advance U.S. national security interests.

Nevertheless, Obama has said Assad must relinquish control if there is to be peace. And Kerry, Clinton's successor as the chief U.S. diplomat, has repeatedly said that to defeat ISIS, the U.S. must be able to assure Syria's many other rebel groups that there will be a post-Assad future for their country.

The dissent document echoes these sentiments, calling the government's barrel bomb attacks on civilians "the root cause of the instability that continues to grip Syria and the broader region."

"Failure to stem Assad's flagrant abuses will only bolster the ideological appeal of groups such as (ISIS)," the document continued, "even as they endure tactical setbacks on the battlefield."

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