A deadly attack on the Syrian village of Treimsa, where monitors say over 150 people were slaughtered, mainly targeted the homes of rebels, the UN mission said Saturday following a visit there.
The village bore signs of having been pounded with heavy weapons, and homes of rebels and activists had borne the brunt of Thursday's attack, a statement from the UN mission said, referring to "pools of blood and blood spatters".
Sausan Ghosheh, spokeswoman for the UN Supervision Mission in Syria, said a team of observers had visited the village in central Syria on Saturday.
"On the basis of this preliminary mission, UNSMIS can confirm that an attack, using a variety of weapons, took place in Treimsa on July 12," she said in a statement, without specifying who may have carried out the attack.
Activists say more than 150 people were killed in the assault which they allege was a massacre carried out by the army, backed by pro-regime militiamen known as shabiha ("ghosts" in Arabic).
The head of the Syrian Observatory for Human Rights (SOHR), Rami Abdel Rahman, told AFP it "might be the biggest massacre committed in Syria since the start of the revolution" against Assad in March 2011.
If confirmed, the toll would exceed that of a massacre at Houla on May 25, when a pro-government militia and government forces were accused of killing at least 108 people.
Syria's military however said the army had killed "many terrorists" in Treimsa, but no civilians, in a "special operation... targeting armed terrorist groups and their leadership hide-outs."
Ghosheh said a "wide range of weapons were used, including artillery, mortars and small arms."
"The attack on Treimsa 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 UN team also observed a burned school and damaged houses with signs of internal burning in five of them."
The number of casualties was still unclear, she added.
The Treimsa killings have triggered a global outcry against the regime of President Bashar al-Assad, with UN chief Ban Ki-moon calling for urgent action to stop the bloodshed.
Ghosheh said the observers planned to return to Treimsa on Sunday for further investigations.
"UNSMIS is deeply concerned about the escalating level of violence in Syria and calls on the government to cease the use of heavy weapons on population centres and on the parties to put down their weapons and choose the path of non-violence for the welfare of the Syrian people who have suffered enough," she said.
Meanwhile an AFP reporter near the northern city of Aleppo said intensive bombardments had been heard for nearly six hours Saturday some 30 kilometres (20 miles) west of the city.
A rebel official who was in radio contact with fighters said the artillery of government forces based at Ourm Assoughra, 20 kilometres west of Aleppo, had pounded the nearby towns of Aljineh, Ibbin and Zardana.
The correspondent said there had been blasts and bursts of shooting every couple of minutes from 1500 GMT to 2100 GMT, dying down to a rate of one explosion every 15 minutes.
The rebel official could not give a death toll but said that "given the intensity of the explosions, it is certain that there are deaths."
The Observatory said earlier that Syrian troops and pro-regime militias had stormed and torched a town in southern Syria on Saturday.
Hundreds of soldiers backed by helicopter gunships attacked Khirbet Ghazaleh in the province of Daraa -- the cradle of a 16-month uprising -- amid heavy gunfire, the watchdog said.
An activist on the ground who identified himself as Bayan Ahmad said pro-regime militias has set alight houses in the town.
"The army entered without resistance as the rebel Free Syrian Army left town. The shelling has wounded dozens of people but we don't have medical resources to treat them," he added.
Elsewhere, a pregnant woman was among 115 people including 50 civilians killed across the country on Saturday, the Observatory said.
An AFP journalist said fighting Saturday near the Turkish border between government troops and rebel fighters had left at least 10 rebels dead and 15 wounded.
The Treimsa killings have added urgency to deadlocked Security Council negotiations on a Syria resolution.
Treimsa is near Al-Kubeir, where at least 55 people were killed on July 6, according to the Observatory. Like Al-Kubeir,
Treimsa is a majority Sunni village situated near Alawite hamlets.
Assad belongs to the Alawite community -- an offshoot of Shiite Islam -- although most Syrians.
UN chief Ban Ki-moon lashed out at the Syrian regime and called for the UN Security Council to urgently act to stop the bloodshed, as failing to do so would give "a licence for further massacres."
Western nations have proposed a resolution that would impose sanctions on the Assad regime over the conflict, which rights activists say has cost more than 17,000 lives.
They also want to give the UN observer mission a new mandate, but for only 45 days. Their mandate ends on July 20.
Russia has rejected as unacceptable any use of sanctions. It is proposing a rival resolution that renews the mandate of UNSMIS for 90 days.