Top US intelligence officials have pointed to al Qaeda in Iraq as the likely culprit behind recent bombings in Syria, the deadliest attacks against the Syrian government in the 11-month uprising.
Though the US has called for Syrian President Bashar Assad to step down, his fall could lead to a power vacuum that al Qaeda's largest regional affiliate or other extremist groups could fill, Director of National Intelligence James Clapper told the US Congress. And that could allow such groups to help themselves to Syria's vast stockpiles of chemical weapons, he said.
At the Pentagon, Defence Secretary Leon Panetta said the crisis in Syria has become "that much more serious" and worrisome to the United States as a result of indications that al Qaeda has infiltrated the government's opposition.
"It does raise concerns for us that al Qaeda is trying to assert a presence there," he said. "As to just what their role is and how extensive their role is, I think that still remains to be seen."
In New York, meanwhile, the UN General Assembly approved a resolution backing an Arab League plan calling for Assad to step down and strongly condemning human rights violations it said his government had committed. The vote, though not legally binding, reflects widespread world opinion.
Likewise, in Vienna, UN Secretary-General Ban Ki-moon accused the Syrian government of committing "almost certain" crimes against humanity as activists reported fresh violence and the arrest of several prominent dissidents, including a US-born blogger.
The comments by Panetta and Clapper in Washington marked a diplomatically dissonant moment of near-agreement between American officials and the Syrian leadership they have called on to step down, after the deaths of thousands of Syrians in the unrest that started during last year's Arab Spring.
Syrian President Assad has long blamed terrorists for starting the uprising, which has pitted his military against a rag-tag group of angry Syrians, divided by religion and neighbourhood.
Al Qaeda's leader called for Assad's ouster last week. That endorsement has created new obstacles for the US, its Western allies and Arab states trying to figure out a way to help push Assad from power.
Clapper said bombings against Syrian security and intelligence targets in Damascus in December, and two more recent bombings in the nation's largest city, Aleppo, bear "all the earmarks of an al Qaeda-like attack," leading the US intelligence to believe the Iraqi militant branch is extending its reach into Syria.
He added the mixture of Syrian opposition groups may have been infiltrated by such militants, probably without their knowledge.
"We've seen evidence of Sunni extremists," he said. "Can't label them specifically as al Qaeda, but similar ilk who are infiltrating the oppositionist groups."
Clapper predicted continued stalemate in Syria, with the opposition too disorganised to present a formidable threat on one side, and Iran providing arms and continued support to prop up the government on the other.
But he warned Assad's fall would be a boon to extremists.
"There is no identifiable group that would succeed him," Clapper said. "So there would be kind of a vacuum, I think, that would lend itself to extremists operating in Syria," who could potentially access the country's multiple chemical weapons sites.
Al Qaeda in Iraq is best positioned to take advantage of that chaos, with its strong family and Sunni religious ties in Syria. The group has long used the country as a transit point to smuggle bombers and bomb-making material over Syria's long desert border with Iraq. During the US war in Iraq, Syrian co-ordinators were able to smuggle fighters back and forth between the two countries.
Clapper said the Iraq-based group "remains capable of high-profile attacks" inside Iraq, and is likely to continue attacking US interests there.
Prior to Clapper's remarks, US intelligence officials had been more circumspect, saying the main trunk of al Qaeda was seeking to ally itself with the Syrian rebels as a way to reinvigorate its overall campaign, so under siege is the group from the CIA drone war in Pakistan and the steady drumbeat of special operations raids and air strikes in Afghanistan, Yemen and Somalia.
Toward that end, core al Qaeda leader Ayman al-Zawahri released a video calling on Muslims to support Syrian rebels over the weekend.
But there has been no discernible rush of would-be attackers to Syria from the outside, added Defence Intelligence Agency chief Lieuteantn General Ronald Burgess at the same hearing.
Clapper also downplayed another recent core al Qaeda announcement of a new union with Somalia based al-Shabab.
"Core al Qaeda is an organisation under siege and is in decline. Al-Shabab, for its part, is under pressure" from both Ethiopian and Kenyan troops, Clapper said. "They've lost territory and are under the gun."