The Arab League has suspended its monitoring mission in Syria and criticised President Bashar al-Assad's regime for the escalating violence that has claimed the lives of at least 80 people in recent days.

In a statement, Nabil el-Araby, the league's secretary general, said around 100 observers would remain in the country but would not undertake new missions.

"Given the critical deterioration of the situation in Syria and the continued use of violence … it has been decided to immediately stop the work of the Arab League's mission to Syria pending presentation of the issue to the league's council," he said.

The league's mission in Syria has faced widespread criticism for failing to bring a halt to the regime's crackdown on protests. Gulf states, led by Saudi Arabia, pulled out of the mission on Tuesday.

The secretary-general and Hamad bin Jassim al-Thani, the prime minister of Qatar, are set to leave for New York to seek UN support for the latest Arab plan to end the Syrian crisis on Sunday.

The plan calls for a two-month transition to a unity government, with Assad giving his vice president full powers to work with the proposed government.

Syria has rejected the proposal, saying it violates its sovereignty. The UN security council began closed-door negotiations on a new Arab-European draft resolution on Friday, but Russia's envoy said he could not back the language as it stands.

In the bloodiest incident reported on Saturday, Syria's state-run Sana news agency said "terrorists" ambushed a bus carrying army officers near the tense Damascus suburb of Douma, killing seven people.