More than 100 people, including 60 army deserters, were killed by Syrian forces in one of the bloodiest massacres of the country's nine-month uprising just as Arab League peace observers are set to enter the country.

Soldiers deserting their army base in the northwestern Idlib province were gunned down by Syrian security forces; more than 60 were killed, the Syrian Observatory for Human Rights reported. Forty civilians had been shot dead elsewhere, it said.

According to opposition forces, the fleeing soldiers' intention was to make a dash for the Turkish border to join the Syrian Free Army, a rebel force made up of fellow defectors. But the plan was either ill-judged or loyalist forces too well prepared, the Daily Telegraph reported.

SANA, the state news agency, said Syrian President Bashar al-Assad called for the death penalty for anyone caught distributing arms with the aim of committing terrorist acts.

Arab League Secretary-General Nabil Elaraby said that an advance team would go to Syria. Up to 150 monitors are due to arrive by the end of the month.

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

On Monday, after weeks of stalling, Syria singed a protocol to accept the monitors who will observe al-Assad's implementation of a peace plan that would see negotiations with the opposition and the withdrawal of the Syrian army to barracks.

At least 5,000 people have died in the uprising, the United Nations said.

In November, Turkey joined the Arab League, the United States and the European Union in imposing sanctions on the Syrian regime.

Assad's government was at an impasse [and] prefers to repress its people rather than engage in democratic reforms, Turkish foreign minister Ahmet Davutoglu said as he announced the suspension of ties with Syria's central bank and the banning of all military sales.

Syria's continued violence against its citizens, and its refusal to heed international calls for a peaceful resolution, has prompted Turkey to suspend relations with its neighbour, he said.

Every bullet fired, every bombed mosque, has eliminated the legitimacy of the Syrian leadership and has widened the gap between us, Davutoglu said. Syria has squandered the last change that it was given.