BEIRUT — U.N. observers investigated the latest reported massacre in Syria, entering a village Saturday where activists say regime forces killed dozens of people the past week.

An 11-vehicle team of observers went into the central village of Tremseh after receiving confirmation a cease-fire was in place, a spokesman for the U.N. mission in Syria, Ahmad Fawzi, said.

It is the first outside look into the village where activists say at least 150 people were killed by government troops who shelled the town before moving in alongside pro-regime militiamen.

“We have sent a large integrated patrol today to seek verification of the facts,” Fawzi said.

Details of the killings remain unclear. The Syrian government says 50 people were killed Thursday when its forces clashed with “armed gangs” that were terrorizing village residents. The regime refers to its opponents as terrorists and gangsters.

On Friday, the United Nations blamed government forces for the Tremseh assault, saying UN observers deployed near the village saw government troops using heavy weaponry and attack helicopters.

Turkey’s prime minister blasted Damascus’ leadership, warning that the Syrian people will “make them pay” for such mass killings.

“These vicious massacres, these attempts at genocide, these inhuman savageries are nothing but the footsteps of a regime that is on its way out,” said Recep Tayyip Erdogan.

The prime minister of Turkey was once an ally of President Bashar Assad before turning against him early on in the uprising over the regime’s bloody crackdown.

Other world leaders have heaped criticism on Assad’s regime over the Tremseh incident, which was the latest in a series of reported mass killings by regime forces in recent months.

Anti-regime activists say more than 17,000 people have been killed since the uprising against Assad’s rule began in March 2011. The killings cast new doubt over the international community’s efforts to find a diplomatic solution to Syria’s crisis.