DAMASCUS (AFP) ― U.N. observers plan to return on Sunday to the Syrian village of Treimsa to pursue their investigations after saying activists and rebels bore the brunt of an army assault that killed more than 150 people.

In fresh violence on Sunday, at least nine people were killed as regime forces shelled several areas across the strife-torn country, a rights watchdog reported.

Following a visit to Treimsa on Saturday, the U.N. Supervision Mission in Syria said heavy weapons were used and homes burned in Thursday’s attack on the central village, but was unable to give casualty figures.

The international community has reacted with outrage to the latest killings, with U.N. chief Ban Ki-moon appealing for urgent action to stop the bloodshed and urging China ― a key ally of Syria ― to “influence” President Bashar al-Assad in ending the conflict.

“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 centers 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,” said UNSMIS spokeswoman Sausan Ghosheh after the U.N. team visited Treimsa.

“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.

Rami Abdel Rahman of the Syrian Observatory for Human Rights said it “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 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,” she said.

“The U.N. team also observed a burned school and damaged houses with signs of internal burning in five of them.”

Treimsa is a majority Sunni village situated near Alawite hamlets. Assad belongs to the Alawite community ― an offshoot of Shiite Islam ― although most Syrians are Sunni.

The killings have added urgency to deadlocked U.N. Security Council negotiations on a Syria resolution.

Ban, who has said that failing to stop the Syrian bloodshed would give Damascus “a license for further massacres,” urged China to influence Assad.

China is a key player in a Security Council dispute over sanctions against Assad. It has backed Russia in rejecting western demands for international action to press Assad.

Ban, who visits China on Monday, “called on China to use its influence to ensure the full and immediate implementation” of the peace plan of U.N.-Arab League envoy Kofi Annan and an international communique which Beijing agreed on June 30 calling for a political transition, a U.N. spokesman said.

Annan himself is meeting on Monday Russian Foreign Minister Sergei Lavrov for talks on the crisis in Syria, Russian news agencies have reported.

The United Nations will on Monday discuss aid needs for Syria at donors meeting in Geneva, officials said, warning that so far only one fifth of a $189 million appeal had been received.

On Sunday, nine people were killed in new violence across Syria, including two civilians when troops shelled the flashpoint city of Homs as they tried to seize control of several neighbourhoods, activists said.

On Saturday a pregnant woman was among 115 people including 50 civilians killed across Syria, said the Observatory.

Meanwhile, the outskirts of the northern commercial hub of Aleppo came under intense bombardment on Saturday, an AFP reporter and a rebel official said.

The Observatory also said that on Saturday troops and militias had stormed and torched the southern town of Khirbet Ghazaleh in the province of Daraa ― cradle of the 16-month uprising.