Activists say an explosion has ripped through a building in the central Syrian city of Hama, killing several people and wounding dozens more.
The opposition Syrian Observatory for Human Rights said at least 12 people had died.
But another anti-government group, the Local Coordination Committee, said 54 were killed when security forces fired a rocket at the building.
euronews is unable to independently verify reports from Syria because the government restricts access to foreign media.
Opposition groups are angry after the UN said it would take another month to deploy one hundred unarmed monitors of a 300-strong team.
Just 11 are already in Syria. France has urged for the observers to be deployed more quickly.
Paris has also refused to rule out harder sanctions against President Bashar Assad’s regime or even military force.
The UN observers are there to monitor Assad’s commitment to a ceasefire pact.
But Damascus says it reserves the right to strike back at what it calls “terrorist groups.”