The U.N. General Assembly on Thursday overwhelmingly approved a resolution demanding that Syria end its brutal 11-month crackdown on protesters and endorsing an Arab League plan for a political transition that would require President Bashar al-Assad to yield some of his power.

The nonbinding resolution is largely symbolic and includes no enforcement provisions. But its approval, by a vote of 137 to 12, with 17 abstentions, highlights the growing isolation of Syria’s closest protectors at the United Nations, particularly China and Russia, which voted against Thursday’s resolution and vetoed a similar measure in the U.N. Security Council two weeks ago.

The new measure calls on U.N. Secretary General Ban Ki-moon to appoint a special envoy for Syria, where more than 6,000 people are estimated to have been killed since the uprising began. It also “strongly condemns” Syria’s crackdown and urges the government to “immediately put an end to all human rights violations and attacks against civilians.”

“Today the U.N. General Assembly sent a clear message to the people of Syria — the world is with you,” Susan Rice, the U.S. ambassador to the United Nations, said in a statement.

Diplomatic efforts to resolve the crisis have been stalled since the Feb. 4 veto of the Security Council resolution, which would have called for the seating of a national unity government in Syria. The Arab League now hopes Thursday’s vote will help reinforce that political plan.

In the meantime, there are still divisions among diplomats over the best course of action to prevent further bloodshed.

France and Turkey have pressed for the establishment of a humanitarian corridor to permit the distribution of assistance to Syrian civilians, a proposal Ban backed on Thursday in discussions with Russian officials.

Obama administration officials have been pressing for more clarity on the proposal. They have pointed out the complications of distributing aid throughout Syria and protecting such a corridor, as well as convincing Russia that it is not a stalking horse for the regime change Moscow has already rejected.

On Thursday, Bashar al-Jaafari, Syria’s U.N. ambassador, denounced the chief Arab and Western sponsors of the new resolution, saying they were “leading a political and media aggression against Syria” and providing logistical and military support for “armed terrorists” seeking to overthrow Assad’s government.

He accused the sponsors of ignoring his country’s offer to introduce political reforms and dismissing a series of Russian amendments aimed at calling on the opposition to dissociate itself with the country’s armed resistance.

In Syria, security forces continued their assault aimed at suppressing the revolt, with attacks across the country killing 26 people, according to the human rights advocacy group Avaaz.

The veto of the Security Council resolution appears to have emboldened the Syrian government to crack down even more harshly against protesters, and the conflict has increasingly taken on the cast of an armed insurgency as frustrated protesters gather weapons and fight back.

In Washington, top U.S. intelligence officials said Thursday that they think members of al-Qaeda have infiltrated Syrian opposition groups, and probably executed recent bombings in the nation’s capital and largest city.

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,” Director of National Intelligence James R. Clapper said at a congressional hearing, adding that the network’s affiliate in Iraq “is extending its reach into Syria.”

But Clapper suggested that al-Qaeda has not sought to call attention to its presence, and that its operatives may have slipped into groups of fighters who oppose 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.

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.”

Correspondent Liz Sly in Beirut and staff writers Greg Miller and Karen DeYoung in Washington contributed to this report.