UNITED NATIONS - UN Secretary General Ban Ki-Moon has expressed his outrage at the latest killing in Syria, warning that any failure by the international community to take action would be “a license for further massacres."

In a letter to the UN Security Council, the UN-Arab League

Special Envoy Kofi Annan said the Syrian government had violated its commitment to stop using heavy weapons in population centres. “Tragically, we now have another grim reminder that the council's resolutions continue to be flouted,” Annan said in the letter. In a tough statement, Ban said, "I condemn, in the strongest possible terms, the indiscriminate use of heavy artillery and shelling of populated areas, including by firing from helicopters. "They also cast serious doubts on President al-Assad's recent expression of commitment to the six-point plan in his meeting with the Joint Special Envoy," he said.

Assad met with international envoy Kofi Annan in Damascus on Monday Meanwhile, US Secretary of State Hillary Clinton has urged the UN Security Council to make clear to Damascus that there would be consequences after the massacre.

Accounts of the attack on the village of Tremseh provide "indisputable evidence that the regime deliberately murdered innocent civilians," she said. "Those who committed these atrocities will be identified and held accountable," Ms Clinton said.

Syrian opposition activists have put the death toll at Tremseh at anywhere from 100 to more than 200 people and said it was the work of government troops and militia allies.

Ms Clinton said the massacre underscored the need for major powers to increase pressure on President Bashar al-Assad's government to allow for a UN-backed political transition plan to move forward.

She said the UN Security Council - where veto-holders Russia and China have thrown the brakes on western efforts to pass more punitive measures against Damascus - should now make clear that there would be consequences for non-compliance.

The UN chief added, “I call upon all member states to take collective and decisive action to immediately and fully stop the tragedy unfolding in Syria. Inaction becomes a license for further massacres.”

The killing in Treimsa has added new urgency to deadlocked Security Council negotiations on a Syria resolution. Russia has rejected western demands for non-military sanctions to be threatened to back Annan's peace efforts.

Ban expressed outrage at the “horrific” killings in Treimsa on Thursday, which he said cast serious doubt on Assad's commitment to an international peace plan.

The UN leader chief condemned “the indiscriminate use of heavy artillery and shelling of populated areas, including by firing from helicopters”.

The council passed two resolutions in April which set up the UN Supervision Mission in Syria (UNSMIS) and demanded that Assad carry out the six-point peace plan he agreed with Annan. The agreement included a halt to the use of heavy weapons.

Annan reaffirmed his call for the council to “send a message to all that there will be consequences for non-compliance” with his plan.

“This is imperative and could not be more urgent in the light of unfolding events,” he added.

UN envoys held more talks overnight in a bid to break their deadlock on a Security Council resolution to renew the UN mission. A vote must be held by July 20 when the mission's 90-day mandate runs out.

A resolution proposed by Britain, France, United States, Germany and Portugal would give Assad 10 days to stop the use of heavy weapons, in line with the Annan plan, or face sanctions. The western nations only want to give UNSMIS a new 45-day mandate.

Russia's rival resolution would renew UNSMIS for 90 days but makes no mention of international measures. The Russian government has said that sanctions are unacceptable and would not be allowed.