The Arab League, which has deepened Assad's isolation by announcing economic sanctions against Damascus, gave Syria until on December 4 to sign an initiative to end the crackdown, Qatar's foreign minister said.

He did not explicitly say when the sanctions would come into force, but said they would be imposed soon if Syria does not sign the deal, which includes Arab monitors to ensure that Damascus abides by a promise to end violence.

The United Nations' top human rights forum has condemned Syria for "gross and systematic" violations by its forces, including executions and the imprisonment of some 14,000 people.

Syria faces deepening international and regional isolation, with the Arab League, the European Union and the United States piling on tougher and tougher sanctions.

Qatar's Foreign Minister Sheikh Hamad bin Jassim al-Thani, who has played a lead role in organising Arab League sanctions, said the League gave Damascus one day to sign its initiative.

China and Russia oppose sanctions and last month scuppered Western efforts to pass a UN Security Council resolution condemning Assad's government.