Opposition activists in Syria suggest that many of those killed in a massacre in Hama province may have been rebel fighters rather than unarmed civilians.
The United Nations said it had confirmed intense fighting on Thursday, including the use of tanks, helicopters and heavy artillery.
Activists initially claimed 200 people, including civilians, died in the village of Tremseh but later said most of those killed were fighters, the BBC reports.
The Syrian government has accused the opposition of staging the incident to rally world opinion against it at a crucial juncture in international diplomacy over Syria.
The United States Secretary of State Hillary Clinton has suggested the Syrian army "deliberately murdered civilians" in Tremseh.
The Syrian army admitted killing a "big number of terrorists" but insists it did not kill any civilians.
There have been no independent accounts of the number of dead or how they were killed.
Time's up for UN observer mission
The mandate for the UN's observer mission to Syria expires on 20 July and council members are locked in debate about a new resolution, which must be passed before the deadline if the mission is to be renewed.
UN Secretary-General Ban Ki-moon has expressed outrage at the latest reported mass killing in Syria and says any failure by the international community to take action would be a licence for further massacres.
Mr Ban says reports of a massacre cast serious doubts on President Bashar al-Assad's commitment to a UN-backed peace plan.
In a letter to the UN Security Council, the international peace envoy, Kofi Annan, says the Syrian government has violated its commitment to stop using heavy weapons in population centres.
The Security Council is now considering a new resolution on Syria that could extend the mission of UN observers there.
But Russia, which has veto power in the Council, is vowing to use it if the resolution is militarily enforceable.