An advanced team preparing the way for peace monitors will arrive in Syria this week, the Arab League chief said on Tuesday, after more than 100 people were killed in one of the bloodiest days of a revolt against President Bashar al-Assad.

Security forces machine-gunned soldiers deserting from their army base in the northwestern Idlib province on Monday, killing more than 60, according to the Syrian Observatory for Human Rights. It said 40 civilians had been shot dead elsewhere.

The state news agency SANA said security forces had killed five terrorists in Deraa province on Monday night. It also said Assad had decreed the death penalty for anyone caught distributing arms with the aim of committing terrorist acts.

Arab League Secretary-General Nabil Elaraby told Reuters in Cairo that an advance team would go to Syria on Thursday, with the 150 monitors due to arrive by end-December.

It's a completely new mission ... and it depends on implementation in good faith, he said.

Syria stalled for weeks before signing a protocol on Monday to accept the monitors who will check its compliance with an Arab plan for 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.

France said it hoped the monitors could carry out their mission quickly. But it also said Assad had a record of broken pledges and that Monday's violence showed there isn't a moment to lose.

For months we have seen Bashar al-Assad not keep to commitments he made to his people and he has increased his efforts to play for time in the face of the international community, Foreign Ministry spokesman Bernard Valero said.

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.

The Syrian authorities have made it hard for anyone to know what is going on in their troubled country. They have barred most foreign journalists and imposed tight curbs on local ones.

The British-based Observatory said three more people had been killed in violence on Tuesday, two in the city of Homs and one in a village in Idlib province, the scene of a sustained military crackdown in the past three days.

State news agency SANA said a captain in the security forces had died of wounds inflicted by terrorists a week ago in the city of Hama.

U.N. TOLL

The United Nations has said more than 5,000 people have been killed in Syria since anti-Assad protests erupted in March, inspired by a wave of uprisings across the Arab world.

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

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

The United States and European Union have already imposed sanctions on Syria, which combined with the unrest itself have pushed the economy into a sharp fall. The Syrian pound fell nearly 2 percent on Tuesday to over 55 pounds per dollar, 17 percent down from the official exchange rate before the crisis erupted.

Elaraby said the Arab sanctions would remain until monitors begin reporting back. Arab ministers would decide the next step.

He said Gulf states would contribute about 60 of a 150-strong monitoring team led by a Sudanese general, which would expect freedom of movement and communication, including access to prisons and hospitals. Journalists would accompany the team.

The Arab League had threatened to ask the U.N. Security Council to adopt its peace plan for Syria, broadening the chances of international action.

Damascus said Russia, its longtime ally and arms supplier, had urged it to sign the protocol on Arab monitors.

As international pressure mounted, the U.N. General Assembly voted to condemn Syria's use of force to quell protests, with Russia and China abstaining instead of voting against.

Arab rulers want to halt a slide towards a possible civil war in Syria that could shake a region already riven by rivalry between non-Arab Shi'ite power Iran and Sunni Arab heavyweights such as Saudi Arabia.

Iran, Syria's key backer, said the agreement to let in observers from the Arab League was acceptable, if not ideal.

The U.S. State Department voiced scepticism. We are really less interested in a signed piece of paper than we are in actions to implement commitments made, a spokeswoman said.

(Additional reporting by Edmund Blair in Cairo, Dominic Evans in Beirut, John Irish in Paris)