Remarks by Director of National Intelligence James R. Clapper are the most definitive to date from a senior Obama administration official on network’s efforts to insert itself into the Syrian uprising. (Chip Somodevilla/Getty Images)

Members of al-Qaeda have infiltrated Syrian opposition groups, and likely executed recent bombings in the nation’s capital and largest city, the United States’ top intelligence official said Thursday.

The remarks by Director of National Intelligence James R. Clapper are the most definitive to date from a senior Obama administration official on al-Qaeda’s efforts to insert itself into the Syrian uprising.

Two bombings in Damascus in December, as well as deadly attacks on security and intelligence buildings in Aleppo last week, “had all the earmarks of an al-Qaeda-like attack,” Clapper said, adding that the network’s affiliate in Iraq “is extending its reach into Syria.”

But Clapper suggested that al-Qaeda has so far not sought to call attention to its presence, and that its operatives may have slipped into groups of fighters opposed to the government of President Bashar al-Assad.

Al-Qaeda extremists “have infiltrated” opposition groups that “in many cases may not be aware they are there,” Clapper said in testimony before the Senate Armed Services committee.

U.S. intelligence agencies have not detected an influx of fighters from neighboring countries into Syria, where opposition forces are fragmented and often feuding, with little indication that a leader will soon emerge, officials said.

So far there has been no “clarion call to outsiders coming in,” said Lt. Gen. Ronald Burgess, director of the Defense Intelligence Agency. “We haven’t seen much of that up to this time, so basically the team that’s on the ground is playing with what it has.”

Burgess’s comments came just days after al-Qaeda leader Aymen al-Zawahiri released a video message urging fighters in Turkey, Iraq, Jordan and Lebanon to mobilize against Assad.

Al-Qaeda has largely been relegated to the sidelines in a series of uprisings across the Arab world over the past year, and its affiliate in Iraq has struggled to regroup after being hunted to near extinction by Shiite militias aligned with the American military “surge.”

U.S. officials for several weeks have been saying that the bombings in Syria bore certain characteristics of previous al-Qaeda operations, but that no definitive evidence had surfaced to establish that link.

Clapper seemed to go a step farther, describing al-Qaeda’s presence among militant groups as “another disturbing phenomenon that we’ve seen.”

Clapper said that the fighting in Syria is likely to remain at a stalemate without external intervention. Assad may see no alternative to extending the crackdown against opposition groups “because of his psychological need to emulate his father,” who controlled the country for decades with a similarly ruthless approach.

Even so, U.S. intelligence agencies have seen indications that members of Assad’s inner circle are already preparing for a possible coup. “We’ve seen signs of some of the senior [leaders] in the Assad regime making contingency plans to evacuate, move families, move financial resources,” Clapper said. “To this point, they’ve held together.”