Peace envoy Lakhdar Brahimi on Saturday will press Syrian officials for a truce, just hours after Lebanese politicians blamed Damascus for the killing of a top security official.
But even as Brahimi arrived in the war-torn country Friday, government jets hammered the rebel-held town of Maaret al-Numan in the northwest, and fighters there accused the regime of using cluster bombs in the attack, echoing claims by one rights group.
Brahimi flew into the Syrian capital on a mission to secure the ceasefire during the four-day Eid al-Adha Muslim holiday from October 26. He is due to meet Foreign Minister Walid Muallem on Saturday.
He is also expected to hold talks with President Bashar al-Assad at a later date.
"We will have discussions here with the government, the political parties and civil society about the situation in Syria," Brahimi said at Damascus airport.
"We will talk about the need to reduce the current violence and about whether it is possible to stop for the occasion of Eid al-Adha."
Brahimi hopes that if all sides in the Syrian conflict agree a truce over Eid, it will be extended to bring some respite in the 19-month conflict that has already killed more than 34,000 people.
UN chief Ban Ki-moon and Arab League head Nabil al-Arabi urged the sides "to heed the call of the special envoy ... for a ceasefire and a cessation of all violence in all its forms during the period of the Eid al-Adha."
Washington also backed the ceasefire call.
"We urge the Syrian government to stop all military operations and call on opposition forces to follow suit," said a State Department statement.
Damascus has said it is ready to discuss the ceasefire proposal with Brahimi. The opposition says it would welcome any truce but insists the regime must first halt its daily bombardments.
But a devastating car bomb blast in neighbouring Lebanon Friday ratcheted up tension in the region.
The blast killed eight people, including a top security official linked to the anti-Damascus camp in Lebanon.
Two of Lebanon's top anti-Damascus political leaders -- former prime minister and opposition chief Saad Hariri and Druze leader Walid Jumblatt -- accused Assad of being behind the attack.
Syrian Information Minister Omran al-Zohbi, however, condemned the attack. "These sort of terrorist, cowardly attacks are unjustifiable wherever they occur," he said.
On the ground, rebels and loyalists of the regime were locked in battle for the northwestern town of Maaret al-Numan on the Damascus-Aleppo highway linking Syria's two biggest cities.
Syrian forces again battered the town a day after strikes on a residential area killed dozens of people, nearly half of them children, rescuers told an AFP reporter at the scene.
The military wants to regain control of the highway to resupply units under fire in Aleppo for the past three months and assist 250 troops besieged in their Wadi Deif base.
Fighter jets flew overhead at high altitude before nosediving and striking targets on the town's outskirts, as helicopter gunships buzzed the area, the correspondent said.
The Syrian Observatory for Human Rights said the aircraft concentrated their firepower on rebel camps near Wadi Deif, also a major storage facility for armour and fuel.
Rebels showed AFP debris from cluster bombs they accused the air force of dropping on residential areas, as well as dozens of others that failed to explode on impact.
Human Rights Watch has accused Syria of using cluster bombs, a charge denied by the military, which insists it does not possess them.
In the central city of Hama, the Syrian army opened fire and used tear gas against anti-regime protesters, said the Britain-based Observatory.
Following weekly Muslim prayers, hundreds of demonstrators took to the streets in several towns and cities, activists said.
"United States, your malice has not had enough of our blood," was the protesters' rallying cry this week, according to the Syrian Revolution 2011 Facebook page.
Syrian activists have long condemned the international community for its failure to take action against Assad's regime.
The Syrian Observatory said at least 99 people were killed in violence across the country on Friday: 36 civilians, 34 soldiers and 29 rebels.
In the latest cross-border incident, Turkish artillery struck back at Syria on Friday after two Syrian shells landed on the country's territory, Turkey's state-run television TRT reported.
The television network said the shells fell into an empty field in Hatay province near the Syrian border. There was no report of casualties.