The U.N. Security Council gave unanimous backing Wednesday to a four-day truce proposed by the international mediator for Syria to mark a major Muslim holiday after he warned that the failure of yet another cease-fire plan would only worsen the fighting.

Yet even this modest effort — the international community's only plan for scaling back the violence — appears doomed.

Previous cease-fire missions have failed, in part because neither Syrian President Bashar Assad nor rebels trying to topple him had an incentive to end their bloody war of attrition. Both sides believe they can still make gains on the battlefield even as they are locked in a stalemate, and neither has faith in negotiations on a political transition.

Lakhdar Brahimi, the U.N.-Arab League envoy to Syria, has proposed that both sides lay down their arms during the Muslim holiday of Eid al-Adha, which begins Friday.

The Security Council is normally divided on Syria, but Assad allies Russia and China joined other council members in endorsing the idea of a temporary truce that is meant to pave the way for talks on ending Syria's 19-month-old conflict.

The response on the ground ranged from lukewarm to downright rejection. Syrian government officials said they were still studying the idea, while Syria's political opposition said it was skeptical of the regime's promises. A rebel commander dismissed the plan as irrelevant and a radical Islamist group fighting alongside the rebels said it won't comply with any truce.

As Brahimi briefed the Security Council, the death toll since the start of the conflict in March 2011 crossed the threshold of 35,000, activists said, and more violence was reported across the country.

Two car bombs killed at least eight bus passengers in the capital Damascus and 12 regime soldiers near a military checkpoint in the north, while regime airstrikes on villages near a besieged army base killed 12 civilians, activists said. They also posted a video showing at least 13 bodies laid out Wednesday in a room in a Damascus suburb, some of them women and children. Each side blamed the other for the deaths.

Brahimi told the Security Council by video conference from Cairo that he hopes a truce will allow humanitarian aid to reach war-stricken areas and start transition talks, said U.N. diplomats who spoke on condition of anonymity because the meeting was private.

However, months of horrific bloodshed and deep distrust between the combatants make it unlikely they will embark on the path outlined by Brahimi. The Syrian opposition says it won't negotiate unless Assad resigns, something the Syrian leader refuses to do.

"The Syrian regime throughout its reign and up until now signs everything but violates everything," Haitham Maleh, a veteran Syrian opposition leader, said after he and others met with Arab League chief Nabil Elaraby in Cairo.

Maleh said there is concern the regime would exploit a cease-fire to take back rebel-held territory. The opposition will not accept any political solution that does not include Assad leaving his post, he said.

Brahimi has served as envoy since September, taking over from former U.N. chief Kofi Annan, who quit after failing to end the Syria fighting. Annan had pushed a six-point plan, including an April 12 cease-fire that was to lead to transition talks but never took hold.

Annan's successor has been blunt about the difficulty of his assignment, trying to lower expectations. He suggested Wednesday that even the holiday truce is a gamble, saying that failure could make the situation in Syria even worse, according to the U.N. diplomat.

Still, the international community has little else to offer. There is no appetite for military intervention, while harsher U.N. action against the regime has been blocked by Russia and China, two Security Council members with veto powers.

U.S. Secretary of State Hillary Rodham Clinton said she supports Brahimi's cease-fire so that "Syrians could celebrate in peace."

"We'd like to see the violence come to an end, there's no doubt about this, and we'd like to see a political transition take hold and begin. We've been calling for that for more than a year," she added.

Few of those involved in the conflict appeared ready to commit to a truce.

Abdelbaset Sieda, head of the main opposition group in exile, the Syrian National Council, said rebel fighters would hold their fire during the holiday unless attacked by regime forces. However, his group has no control over rebels fighting on the ground.

Rebel commander Zahran Aloush of the al-Islam brigade outside of Damascus said he's ignoring truce efforts. "How can I expect a cease-fire from a regime that has never given us anything, ever," he said via Skype.

The al-Qaida-linked group Jabhat al-Nusra, which fights with the rebels and has claimed a number of large suicide bombings against regime targets, said it will not lay down arms.

"There will be no truce between us and the prideful regime and shedder of the blood of Muslims," the group said in statement posted on militant websites. "We are not among those who allow the wily to trick us, nor are we ones who will accept to play these filthy games."

In Damascus, Foreign Ministry spokesman Jihad Makdessi said the truce proposal was still "being studied" by Syrian army leaders and that Syria's decision would be announced Thursday.

Russia's U.N. Ambassador Vitaly Churkin told reporters after the Security Council meeting that his country had received indications from Syria it would abide by a cease-fire.

Brahimi hasn't said how compliance would be monitored. Annan's truce plan was more comprehensive, calling for an open-ended truce, a pullback of troops and heavy weapons from urban centers and supervision by U.N. monitors.

In Wednesday's violence, 20 people were found dead in a building in the Damascus suburb of Douma, said local activist Mohammed Saeed, speaking via Skype. The dead included 10 women and four children, he said.

An amateur video posted online showed bodies scattered on the landings of a stairwell and sprawled out on tile floors. Among the bodies were those of two young boys, one with a hole in his head, and a woman. A thick stream of blood flowed from a doorway. Another video showed 13 bodies wrapped in blankets and laid out in two rows.

The videos matched activist descriptions of the event, but because Syria imposes tight restrictions on foreign journalists, their authenticity could not be independently verified.

The state-run news agency SANA quoted the Foreign Ministry as saying that 25 people were killed in Douma on Wednesday and that they were victims of a massacre carried out by "armed terrorists," the regime's term for opposition fighters.

Also Wednesday, Russia's chief military officer said Syrian rebels have acquired portable air defense missiles, including U.S.-made Stinger missiles. In remarks carried by Russian news agencies, Gen. Nikolai Makarov didn't say how many such missiles the rebels had and who supplied them.

A Syrian rebel told The Associated Press in Turkey that the insurgents obtained dozens of shoulder-fired anti-aircraft missiles, but would not say who provided them.

The Syrian opposition has urged its foreign backers to send heavy weapons, saying rebel fighters cannot break the stalemate as long as Assad can bomb them from the air. However, the Obama administration has refused to do so, saying the weapons might fall into the wrong hands and eventually be used against the U.S. and its allies.

In Washington, State Department spokeswoman Victoria Nuland denied that the U.S. has provided any Stingers to Syrian rebels. She challenged Russia to provide evidence suggesting otherwise.


Associated Press writers Edith M. Lederer at the United Nations, Maggie Fick in Cairo, Bradley Klapper in Washington and Vladimir Isachenkov in Moscow contributed reporting.