A government airstrike on a bakery in a rebel-held town in central Syria killed more than 60 people on Sunday, activists said, casting a pall over a visit by the international envoy charged with negotiating an end to the country's civil war.

The strike on the town of Halfaya left scattered bodies and debris up and down a street, and more than a dozen dead and wounded were trapped in a tangled heap of dirt and rubble.

The attack appeared to be the government response to a newly announced rebel offensive seeking to drive the Syrian army from a constellation of towns and village north of the central city of Hama. Halfaya was the first of the area's towns to be "liberated" by rebel fighters, and activists saw Sunday's attack as payback.

"Halfaya was the first and biggest victory in the Hama countryside," said Hama activist Mousab Alhamadee via Skype. "That's why the regime is punishing them in this way."

The total death toll remained unclear, but the Britain-based Syrian Observatory for Human Rights said more than 60 people had been killed. That number is expected to rise, it said, because some 50 of those wounded in the strike are in critical condition.

Mound of human flesh

Amateur videos posted online Sunday showed residents and armed rebels rushing to the scene. One stopped to cover a mound of human flesh lying in the street with his coat.

More than a dozen dead or seriously wounded people lay in the street near a simple concrete building, some in puddles of blood. Near its front wall, bodies jutted from a pile of dirt and rubble on the sidewalk.

Rebels screamed in distress while trying to extract the bodies, while others carried away the wounded.

It was unclear from the videos whether the building was a bakery. Nearly all the dead and wounded appeared to be men, some wore camouflage, raising the possibility that the jet had targeted a rebel gathering.

For the past week, rebels have been launching attacks in the area, most notably in the nearby village of Morek, where they hope to seize control of the country's main north-south highway, preventing the regime from getting supplies to its forces further north in the provinces of Idlib and Aleppo.

On Saturday, one rebel group threatened to storm two predominantly Christian towns nearby if their residents did not "evict" government troops they said were using them as a base to attack nearby areas.

UN envoy arrives in Damascus

The activist accounts could not be independently verified due to restrictions on reporting in Syria. The government of President Bashar al-Assad does not respond to requests for comment on its military activities.

The attack coincided with the start of a two-day visit by Lakhdar Brahimi, who represents the UN And the Arab League, to meet with top Syrian officials.

Brahimi has made little apparent progress toward ending Syria's crisis since assuming his post in September, mostly because the sides appear more interested in fighting it out than in sitting down for talks.

Brahimi did not speak publicly upon arriving in Damascus for a two-day mission, and it was unclear whether he would present new ideas to end the war. His trip appeared troubled from the start.

Instead of flying directly to Syria as he had on previous visits, Brahimi landed in Beirut and travelled to the Syrian capital by land because of fighting near the Damascus airport, Lebanese officials said.

The Lebanese officials, who spoke on condition of anonymity, said Brahimi was expected to meet Syria's foreign minister later Sunday and Assad on Monday.

The trip is Brahimi's third since taking the job following the resignation of former UN Secretary General Kofi Annan after both sides disregarded a cease-fire he brokered in April. While not advancing a comprehensive peace plan, Brahimi has called on the sides to negotiate a solution.

With files from The Associated Press