The UN General Assembly voted overwhelmingly Thursday for a resolution backing an Arab League plan calling for Syrian President Bashar al-Assad to step down and strongly condemning human rights violations by his regime.

The vote in the 193-member world body on the Arab-sponsored resolution was 137-12 with 17 abstentions. Several countries complained immediately afterward that they unable to vote due to problems with the UN's voting machine.

Supporters were hoping for a high "yes" vote to deliver a strong message to Assad to immediately stop the bloody crackdown that has killed over 5,400 people and hand power to his vice-president. The measure had over 70 co-sponsors and won support from more than two-thirds of the General Assembly.

"Today, the UN General Assembly sent a clear message of the people of Syria: the world is with you," U.S. Ambassador Susan Rice said in a statement. "A rapid transition to democracy in Syria has garnered the resounding support of the international community. Change must now come."

'We see almost a certain crime against humanity.'—UN secretary general Ban Ki-moon

Hours before the vote was held, UN secretary general Ban Ki-moon accused the Syrian regime of potential crimes against humanity as activists reported fresh violence in Deraa, the city where the uprising against Assad erupted 11 months ago.

Speaking in Vienna, Ban demanded the Syrian regime stop using indiscriminate force against civilians caught up in fighting between government troops and Assad's opponents.

"We see neighbourhoods shelled indiscriminately, hospitals used as torture centres, children as young as 10 years old chained and abused," he said. "We see almost a certain crime against humanity."

Resolution not legally binding

There are no vetoes in the General Assembly and while their resolutions are not legally binding, they do reflect world opinion on major issues.

The transfer of power to Syria's vice-president is part of the Arab League plan for a transitional government which was adopted on Jan. 22. It calls for the establishment of a national unity government within two months to prepare for internationally supervised parliamentary and presidential elections.

Russia and China, who vetoed a similar resolution in the Security Council, voted against the General Assembly measure along with North Korea, Iran, Venezuela, Cuba and others who heeded Syria's appeal to vote "no."

Black smoke rises from Syrian oil refinery at Homs on Wednesday. The UN secretary general has denounced the Syrian regime for potential crimes against humanity. (Reuters)

Syria's UN Ambassador Bashar Ja'afari warned that the resolution will send a message to extremists that "violence and deliberate sabotage" are acceptable and will lead "to more chaos and more crisis."

Russia's Deputy Foreign Minister Gennady Gatilov called the assembly resolution "unbalanced," saying "it directs all the demands at the government, and says nothing about the opposition," according to Russian news agencies.

The resolution condemns "all violence, irrespective of where it comes from, and calls upon all parties in Syria, including armed groups, to immediately stop all violence or reprisals," as called for by the Arab League.

Russia proposed ammendments

But Arab countries on Tuesday rejected amendments proposed by Russia, which has been one of Syria's strongest backers since the Cold War when the president's late father, Hafez al-Assad, led the country.

Russia's UN Ambassador Vitaly Churkin said his country voted against the resolution because its proposed amendments were ignored.

One called on "all sections of the Syrian opposition to dissociate themselves from armed groups engaged in acts of violence" and urged countries with influence to prevent continued violence by such groups. The other demanded that the withdrawal of all Syrian armed forces from cities and towns — which is called for in the Arab League plan — take place "in conjunction with the end of attacks by armed groups against state institutions and quarters of cities and towns."

Arab sponsors couldn't accept these amendments because they sought to equate the Assad regime's crackdown on civilian protesters with the opposition that rose up to confront the violent attacks. UN diplomats said, speaking on condition of anonymity because the discussions were private.

Churkin stressed that the key to resolving the Syrian crisis is "through an inclusive political process led by the Syrians themselves."

Thursday's vote came as the U.S. raised concerns that an al-Qaeda-linked group may have joined in the uprising against Assad's regime.

Senior U.S. intelligence officials said Thursday that al-Qaeda in Iraq was the likely culprit behind recent bombings in Syria, the deadliest attacks against the Syrian government since the unrest began 11 months ago.

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.