An explosion ripped through a building in Syria’s central city of Hama on Wednesday, killing at least 12 people and wounding dozens more, the opposition Syrian Observatory for Human Rights said, in a bloody violation of a shaky cease-fire in the country.

The grassroots Local Coordination Committee said security forces fired a rocket at the building and put the death toll much higher, with 54 dead, several of them children.

Footage on YouTube of the blast showed a crowd of men pulling the bloodied body of a young girl from the rubble, shouting “God is great.”

Another video shows the collapsed remains of the building, as ash-covered men dig through piles of masonry looking for bodies amid the cries of onlookers.

An activist who asked not to be named said the blast may have been an explosion from inside the building.

Hama, a hotbed of revolt in the year-long uprising against President Bashar Assad’s rule, has a small team of United Nations observers, who are preparing the way for a larger UN mission which will monitor the peace plan brokered by UN-Arab League envoy Kofi Annan two weeks ago.

Two days ago, activists said Syrian forces shelled another district of Hama, killing at least 20 people and wounding more than 60.

There was no immediate comment from Syrian authorities who say they are committed to international mediator Kofi Annan’s April 12 cease-fire agreement, but reserve the right to respond to what they say are continued attacks by “terrorist groups.”

Hama is a particularly sensitive site for the opposition. Assad’s father, Hafez Assad, crushed an armed Islamist uprising in Hama 30 years ago, killing many thousands of people and flattening parts of Hama’s old city.