For the United States, Syria's civil war is threatening to start hitting closer to home.
Peace talks between the Syrian government and opposition are faltering. President Bashar Assad's military is on the offensive and the rebels are in disarray. Most distressing to the Obama administration, U.S. officials say al-Qaida-linked militants are squeezing moderates out of the insurgency and carving out havens for potential terrorist plots against the United States.
The accelerating U.S. national security threat is leading the administration to take a fresh look at previously shelved ideas, including more robust assistance to Western-backed rebels.
They are also are looking at newer, more far-reaching options, including drone strikes on extremists and more forceful action against Assad, whom President Barack Obama told to leave power 30 months ago.
Obama's top aides plan to meet at the White House before week's end to examine options, according to administration officials. They weren't authorized to talk publicly on the matter and spoke only on condition of anonymity.
"We have to examine what the alternatives some might be proposing are and whether they're in our national security interest," White House press secretary Jay Carney told reporters Tuesday. He expressed concern about stepped-up intervention leading to "unintended consequences."
For all the talk about policy changes, American officials remain hampered by the same constraints that have stymied the U.S. response throughout the three-year civil war, including concern that lethal assistance could end up in the hands of extremists. And then there also is Obama's own distaste for military action.
After more than a decade of fighting in Afghanistan and Iraq, Obama has desperately sought to avoid embroiling the U.S. in another deadly and inconclusive war. He backed away last year from his threat to take military action in response to a Syrian chemical weapons attack when it became clear Congress would not vote its approval.
Even options short of direct strikes pose difficulties.
Grounding Assad's air force by enforcing a no-fly zone in Syria would most likely require a large-scale attack on the military's advanced air defense systems. Military support for the opposition continues in the form of small weapons and ammunition. But proposals for sending more powerful weaponry raise fears that it could fall into the hands of extremist rebel groups, which are melding with moderate rebels.
The U.S. remains opposed to Saudi Arabian deliveries of shoulder-launched, anti-aircraft missiles because of the potential risk to commercial aircraft.
"Right now we don't think that there is a military solution," Obama said last week following talks on Syria with French President Francois Hollande. At the same time, Obama called the situation on the ground "horrendous" and acknowledged "enormous frustration" with peace talks in Geneva, which ended last weekend without progress.
By any account, the U.S. policy of sending limited military aid for Syria's moderate opposition coupled with support for U.N.-brokered peace talks between the rebels and Assad's government isn't working.
Appalling scenes of emaciated children leaving the besieged city of Homs last week underscored the desperate plight of many Syrians — and the potential for more suffering. A second round of Geneva negotiations ended last weekend with little promise for a future breakthrough and with fresh American frustrations with Russia, which is Assad's most powerful military and diplomatic supporter.
The administration concedes Assad's hold on power has strengthened.
On Tuesday, Secretary of State John Kerry offered lingering hope that peace talks could yield results.
However slowly, the potential for a terrorist base developing in northern Syria akin to Afghanistan before the Sept. 11, 2001, attacks may be changing the administration's thinking.
In recent weeks, the president's senior national security aides have delivered dire warnings about extremist havens in Syria and about Americans and other Westerners joining the fight and being radicalized.
Testifying before Congress this month, National Intelligence Director James Clapper estimated there were about 26,000 extremists in Syria, including around 7,000 foreigners, in an insurgency encompassing 75,000 to 110,000 fighters. For example, Jabhat al-Nusra, one of the most powerful rebel factions, has "aspirations" for attacks on the United States, he said.
In addition to worries about foreigners, officials cite concerns about small numbers of Americans who've fought in Syria and returned home. The officials describe these as a "handful," with European countries facing "several dozen" similar cases. But they believe some were probably recruited by extremists, indoctrinated and provided terror training. And more Americans may be heading over to fight.
The stark assessments have prompted questions from Congress about potential action. So far, the administration hasn't provided answers.
U.S. officials said missile strikes by drone or military aircraft against al-Qaida-linked forces have been considered, even if they are unlikely in the near future. The Pentagon has advised against any such strikes because of sketchy U.S. intelligence on the rebel forces in Syria, according to two U.S. officials.
To monitor the threat, officials said, the U.S. and its allies are trying to track any Western fighter returning home from Syria.