UN spokeswoman Sausan Ghosheh confirmed reports that a group of observers had entered Tremseh with a convoy of about a dozen vehicles after being informed of a cease-fire on Friday.

The UN's observers said that the attack appeared to target the homes of rebels, conflicting with reports that the attack was entirely indiscriminate.

"A wide range of weapons were used, including artillery, mortars and small arms," Ghosheh said in a statement.

"The attack on Tremseh appeared targeted at specific groups and houses, mainly of army defectors and activists. There were pools of blood and blood spatters in rooms of several homes together with bullet cases."

The head of the Syrian Observatory for Human Rights, Rami Abdel Rahman, told the AFP news agency that the Tremseh killings "might be the biggest massacre committed in Syria since the start of the revolution" in March 2011. If confirmed, the toll would exceed that of a May 25 massacre at Houla, when militia and government forces were accused of killing at least 108 people.

A spokesman for Syria's military said the army killed "many terrorists" in a "special operation ... targeting armed terrorist groups and their leadership hide-outs." The spokesman said that the pro-Assad forces had not killed any civilians.

Tremseh, population 7,000, is a mainly Sunni Muslim village lying near al Qubeir. Opposition groups say that at least 55 people had been already been killed earlier this month by Assad's forces and paramilitaries.

'Attempted genocide'

In Turkey, Prime Minister Recep Tayyip Erdogan told a meeting of his Justice and Development Party that "this inhuman massacre, this attempted genocide, are just early signs pointing to the demise of this regime." He added that "all dictators are cowards ... Sooner or later, these cruel despots will go and the people will want a settling of accounts."

Turkey's ties with its neighbor Syria have disintegrated during the uprising, with Erdogan consistently among Assad's harshest critics - even before the downing of a Turkish warplane last month.

Pro-Assad forces reportedly killed up to 28 people around the country on Saturday. Shelling and fighting were reported in the central province of Homs. Khirbet Ghazaleh, a rebel stronghold in the southern province of Daraa, was said to be under siege by hundreds of government troops backed by helicopter gunships and armored vehicles.

Severe restrictions placed on journalists have made it virtually impossible to independently confirm these and other casualty figures being reported in the country.

mkg/msh (AFP, dpa, AP)