BEIRUT (AP) -- Syria's air force fired missiles and dropped barrel bombs on rebel strongholds while opposition fighters attacked regime positions Sunday, flouting a U.N.-backed cease-fire that was supposed to quiet fighting over a long holiday weekend but never took hold.

The failure to push through a truce so limited in its ambitions -- just four days -- has been a sobering reflection of the international community's inability to ease 19 months of bloodshed in Syria. It also suggests that the stalemated civil war will drag on, threatening to draw in Syria's neighbors in this highly combustible region such as Turkey, Lebanon and Jordan.

"This conflict has now taken a dynamic of its own which should be worrying to everyone," said Salman Shaikh, director of the Brookings Doha Center think tank.

The U.N. tried to broker a halt to fighting over the four-day Eid al-Adha Muslim feast that began on Friday, one of the holiest times of the Islamic calendar. But the truce was violated almost immediately after it was supposed to take effect, the same fate other cease-fires in Syria have met.

Activists said at least 110 people were killed Sunday, a toll similar to previous daily casualty tolls. They include 16 who died in an airstrike on the village of al-Barra in northern Syria's mountainous Jabal al-Zawiya region.

The Observatory also reported a car bomb that exploded in a residential area in the Damascus neighborhood of Barzeh and wounded 15 people, but the target was not immediately clear.

Though Syria's death toll has topped 35,000, the bloodiest and most protracted crisis of the Arab Spring, the West has been wary of intervening. There is concern about sparking a wider conflagration because Syria borders Israel and is allied with Iran and the powerful Lebanese militant group Hezbollah.

There are already increasing incidents of the civil war spilling across borders.

Many in Lebanon blame Syria and Hezbollah for the Oct. 19 car bomb that killed the country's intelligence chief. The assassination stirred up deadly sectarian tensions in Lebanon, where Sunnis and Shiites are deeply divided over the Syrian civil war, raising the specter of renewed sectarian fighting.

Lebanon's two largest political coalitions have lined up on opposite sides of Syria's civil war. Hezbollah and its partners who dominate the government have stood by Assad's regime, while the Sunni-led opposition backs the rebels seeking to topple the Syrian government. Assad and many in his inner circle are Alawites -- an offshoot of Shiite Islam and a minority in Syria -- while the rebels come mostly from the country's Sunni majority.

Iraqi Shiites also increasingly fear a spillover from Syria. Iraqi authorities on Sunday forced an Iranian cargo plane heading to Syria to land for inspection in Baghdad to ensure it was not carrying weapons, the second such forced landing this month. The move appeared aimed at easing U.S. concerns that Iraq has become a route for shipments of Iranian military supplies that could help Assad battle rebels.

In Jordan, concern over stability was underlined last month, when its U.S., British and French allies quickly dispatched their military experts to help Jordanian commandos devise plans to shield the population in case of a chemical attack from neighboring Syria.

Turkey's support for the Syrian rebel movement is another point of tension, and Turkey has reinforced its border and fired into Syria on several occasions recently in response to shells that have landed from Syria inside Turkish territory.

The U.S. administration says it remains opposed to military action in Syria and politicians have been preoccupied this year with the presidential election, now a few weeks away.

On Sunday, Syrian warplanes struck the eastern Damascus suburbs of Arbeen, Harasta and Zamalka to try to drive out rebels, according to activists in those areas and the Britain-based Syrian Observatory for Human Rights, which compiles information from activists in Syria.

In Douma, another Damascus suburb, rebels wrested three positions from regime forces, including an unfinished high-rise building that had been used by regime snipers, according to the Observatory and Mohammed Saeed, a local activist.

Fighting was also reported near Maaret al-Numan, a strategic town along the Aleppo-Damascus highway that rebels seized earlier this month. Opposition fighters including the al-Qaida-inspired Jabhat al-Nusra, have also besieged a nearby military base and repeatedly attacked government supply convoys heading there. The Observatory said the Syrian air force fired missiles and dropped barrel bombs -- makeshift weapons made of explosives stuffed into barrels -- on villages near the base.

The cease-fire was seen as a long shot from the outset. International peace envoy Lakhdar Brahimi failed to get firm commitments from all combatants, and no mechanism to monitor violations was put in place.

Jabhat al-Nusra rejected the truce outright. In a video posted this week, the leader of al-Qaida, Ayman al-Zawahri, urged Muslims everywhere to support Syria's uprising.

"It's not just about the Syria military and the army defectors that form the backbone of the Free Syrian Army rebel group anymore," said Hassan Abdul-Azim, a Damascus-based opposition leader. He said there were so many foreign fighters and external actors now involved in the Syrian civil war that only an agreement among the various international and regional powers could put an end to the fighting.

"The truce was merely an attempt by Brahimi to try and temporarily ease the people's suffering in the lost time until the U.S. elections, in the hope that the international community can then get its act together and agree on a diplomatic solution for Syria," he told The Associated Press.

But with the unraveling of the cease-fire, it's unclear what the international community can do next.

Assad allies Russia and China have shielded his regime against harsher U.N. Security Council sanctions, while the rebels' foreign backers including neighboring Turkey have shied away from military intervention. Iran, which is embroiled in its own diplomatic standoff with the West over its suspect nuclear program, is also a staunch supporter of Assad's regime.

The U.S., meanwhile, is averse to sending strategic weapons to help the rebels break the battlefield stalemate, fearing they will fall into the hands of militant Islamists, who are increasingly active in rebel ranks.

"There has been a lack of desire to take the tough decisions," said Shaikh.

"In Washington, they've only been focused on the narrow political goal of their own elections, trying to convince a war-wary public inside the U.S. that we are actually disengaging from the conflicts of the Middle East," he said.

The truce was called as the two sides were battling over strategic targets in a largely deadlocked civil war. They include a military base near a main north-south highway, the main supply route to Aleppo, Syria's largest city, where regime forces and rebels have been fighting house-to-house. It appears each side feared the other could exploit a lull to improve its positions.

Brahimi has not said what would follow a cease-fire. Talks between Assad and the Syrian opposition on a peaceful transition are blocked, since the Syrian leader's opponents say they will not negotiate unless Assad resigns, something he has always refused to do.

In April, Brahimi's predecessor as Syria mediator, former U.N. chief Kofi Annan, tried to launch a more comprehensive plan -- an open-ended cease-fire to be enforced by hundreds of U.N. monitors, followed by talks on a political transition. Annan's plan failed to gain traction, and after an initial decrease in violence, his proposed cease-fire collapsed.

On Sunday, amateur videos posted online showed warplanes flying over the eastern suburbs of Damascus. One video showed two huge clouds of smoke rising from what was said to be Arbeen, and the sound of an airplane could be heard in the background. It was not clear if the video showed the aftermath of shelling or an airstrike.

Another video showed destruction inside the Sheikh Moussa mosque in Harasta. Windows and doors were blown out, glass and debris scattered across the mosque's floor. The narrator broke down as he was heard saying: "Where are the Muslims? Our mosques are being bombed and no one cares."

The videos appeared consistent with Associated Press reporting in the area.

The Syrian government has accused the rebels of violating the cease-fire from the start. The state-run news agency SANA said opposition fighters carried out attacks in a number of areas, including in Aleppo and the eastern town of Deir el-Zour.

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Associated Press writer Karin Laub contributed reporting.