BEIRUT: Syrian forces killed 111 people ahead of the start of a mission to monitor President Bashar al-Assad's implementation of an Arab League peace plan, activists said on Wednesday, and France branded the killings an "unprecedented massacre".

Rami Abdulrahman of the Syrian Observatory for Human Rights said 111 civilians and activists were killed in addition to over 100 casualties among army deserters in Idlib province, turning Tuesday into the "bloodiest day of the Syrian revolution".

"There was a massacre of an unprecedented scale in Syria on Tuesday," said French foreign ministry spokesman Bernard Valero. "It is urgent that the U.N. Security Council issues a firm resolution that calls for an end to the repression."

The main opposition Syrian National Council demanded international action to protect civilians.

The escalating death toll in nine months of popular unrest 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 imposed to push him onto a reform path.

Idlib, a northwestern province bordering Turkey, has been a hotbed of protest during the revolt, inspired by uprisings across the Arab world this year, and has also seen escalating attacks by armed insurgents against his forces.

The Observatory said rebels had damaged or destroyed 17 military vehicles in Idlib since Sunday and killed 14 members of the security forces on Tuesday in an ambush in the southern province of Deraa, where anti-Assad protests began in March.

Events in Syria are hard to verify because authorities have banned most independent reporting. But Tuesday's bloodshed brought the death toll reported by activists in the last 48 hours to over 200.

ARAB PEACE MONITORS

The main opposition Syrian National Council said 250 people had been killed on Monday and Tuesday in "bloody massacres", and that the Arab League and United Nations must protect civilians.

It 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.

Arab League Secretary-General Nabil Elaraby said on Tuesday that an advance observer team would go to Syria on Thursday to prepare the way for 150 monitors due to arrive by end-December.

Syria stalled for weeks before signing a protocol on Monday to admit the monitors, who will check its compliance with the plan mandating an end to violence, withdrawal of troops from the streets, release of prisoners and dialogue with the opposition.

"In a week's time, from the start of the operation, we will know (if Syria is complying)," Elaraby said.

Syrian pro-democracy activists are deeply sceptical about Assad's commitment to the plan, which, if implemented, 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 which he has deployed to crush the mainly Sunni Muslim protests.

In recent months, peaceful protests have increasingly given way to armed confrontations, often led by army deserters.

Some opposition leaders have called for foreign military intervention to protect civilians from Assad's forces.

In a show of military power, state television broadcast footage of live-fire exercises held by the navy and air force, which it said aimed at deterring any attack on Syria.

U.N. TOLL

The United Nations has said more than 5,000 people have been killed in Syria since anti-Assad protests broke out in March, encouraged by other street uprisings in the Arab world that have overthrown dictators in Tunisia, Egypt and Libya to date.

Several weeks ago Damascus said 1,100 members of the security forces had been killed by "armed terrorist gangs". The armed insurrection against Assad has gathered pace since then.

Syria agreed to the Arab peace plan in early November, but the violence continued, prompting Arab states to announce financial sanctions and travel bans on Syrian officials.

The United States and European Union have imposed sanctions on Syria, which combined with the unrest itself have sent the economy into a sharp decline. The Syrian pound fell nearly 2 percent on Tuesday to more than 55 pounds per dollar, 17 percent down from the official rate before the crisis started.

Arab rulers are keen to prevent a descent into civil war in Syria that could affect a region already riven by rivalry between non-Arab Shi'ite Muslim power Iran and Sunni Muslim Arab heavyweights such as Saudi Arabia.