Syrian troops on Thursday pursued an offensive in a region where activists reported the deadliest assault in a nine-month-old crackdown on unrest, as the vanguard of an Arab League team set to monitor compliance with a peace plan headed for Damascus.

The Syrian Observatory for Human Rights said two people were killed in gunfire during a raid on a village by the army and security forces on Thursday, while soldiers backed by tanks and armoured troop carriers swept into the town of Khan Sheikhoun.

Two days earlier Syrian forces had killed 111 civilians and activists in the northwestern province of Idlib bordering Turkey, the British-based Observatory said, an attack that France condemned as an unprecedented massacre.

Over 100 army deserters were killed or wounded, according to the Observatory.

The United States said Syrian authorities under President Bashar al-Assad had flagrantly violated their commitment to end violence while former ally Turkey condemned Syria's policy of oppression which has turned the country into a bloodbath.

Thursday's violence shortly before the expected arrival in Damascus of Arab League officials to prepare for a monitoring mission tasked with ensuring Assad makes good on his commitment to a League plan to end the bloodshed.

The plan entails a withdrawal of troops from the streets, release of prisoners and dialogue with the opposition.

Arab League sources have said the advance team, led by top League official Samir Seif al-Yazal, would comprise about 10 people, including financial, administrative and legal experts to ensure monitors have free access across Syria.

The main group of around 150 observers is to arrive by the end of December. Syria stalled for six weeks before signing a protocol on Monday to admit the monitors.

Events in Syria are hard to verify because authorities, who say they are battling terrorists who have killed more than 1,100 soldiers and police, have banned most independent reporting.

The United Nations said last week that Assad's crackdown had killed more than 5,000 people. Hundreds more have died since then and the escalating death toll has raised the spectre of civil war in Syria with Assad, 46, still trying to stamp out protests with troops and tanks despite international sanctions.

Idlib has been a hotbed of the protest movement, inspired by uprisings across the Arab world this year. Like other centres of unrest, it has seen peaceful protests increasingly giving way to armed confrontations, often led by army deserters.

A politician in neighbouring Lebanon said Assad was trying to crush opposition in the area before the arrival of the monitors to prevent any de facto buffer zone emerging near the Turkish border.

In the southern province of Deraa, where the uprising first erupted, tanks entered the town of Dael on Wednesday, activists said, leading to clashes in which 15 security force members were killed. Six army defectors and a civilian died and dozens of civilians were wounded, they said.

ARAB PEACE MONITORS

The main opposition Syrian National Council (SNC) said 250 people had been killed on Monday and Tuesday in bloody massacres, including a local imam it said was beheaded. It urged the Arab League and United Nations to protect civilians.

The SNC demanded an emergency U.N. Security Council session to discuss the (Assad) regime's massacres in Jabal al-Zawiyah, Idlib and Homs, in particular and called for safe zones to be set up under international protection.

It also said those regions should be declared disaster areas and urged the International Red Crescent and other relief organisations to provide humanitarian aid.

Syrian officials say over 1,000 prisoners have been freed since the plan was agreed six weeks ago and that the army has pulled out of cities. The government promised a parliamentary election early next year as well as constitutional reform which might loosen the ruling Baath Party's grip on power.

Syrian pro-democracy activists are deeply sceptical about Assad's commitment to the plan. If implemented, it could embolden demonstrators demanding an end to his 11-year rule, which followed three decades of domination by his father.

Assad is from Syria's minority Alawite sect, an offshoot of Shi'ite Islam, and Alawites hold many senior posts in the army that he has deployed to crush the protests mounted mainly by members of the country's Sunni Muslim majority.

(Additional reporting by Ece Toksabay in Ankara)