Countries from Australia to the UK have expelled Syrian diplomats in a coordinated move to step up pressure against the regime.
Syrian troops have shelled the central city of Homs in an apparent violation of an internationally brokered ceasefire, activists said.
Five protesters killed in Syria and UN envoys meet to vote on a resolution authorising the deployment of 30 UN observers to the country.
A spokesman for the UN special envoy Kofi Annan says the peace plan for Syria is "on track", after signs of compliance, although slow and small.
UN-Arab League envoy Kofi Annan is expected to tell the UN security council that there is a need for a "stronger presence" of monitors with flexibility in Syria, according to Reuters news agency.
The United Nations should send 300 monitors to Syria as soon as possible to try to stop a wave of killing and violence that a ceasefire has failed to halt, a spokesman for UN-Arab League envoy Kofi Annan said.
Seven unarmed U.N. observers are in Syria monitoring aweek-old truce, with two to follow on Monday, and the full advance team of 30due to be deployed in the coming week, the spokesman, Ahmad Fawzi, said.
But preparations are already under way for the arrival of up to 300 more observers, whose deployment he said he hoped the U.N. Security Council would approve in the next two to three days.
The United Nations has yet to reach an agreement with Damascus on the use of crucial aircraft by an expanded UN ceasefire monitoring mission in Syria, UN Security Council envoys told Reuters.
Amateur footage captures shelling in the Syrian city of Homs as a week-old ceasefire has yet to halt violence in the worst-hit parts of the country.
Reuters have reported Joint special envoy on Syria Kofi Annan has told the UN Security Council that a "bigger" Syrian observer mission is needed immediately, despite ongoing violence. Mr Annan told the Council that swift deployment of more observers could change the political dynamics.
UN observers have arrived in areas of Syria, as activists claim that rebel stronghold areas have been bombarded by heavy shelling.
The Syrian government have signed a UN agreement allowing a ceasefire monitoring mission to take place in the country. Military observers said they would stay in Syria until the "task has been completed", but would not discuss the matter further.
Syria and the United Nations have signed an agreement in Damascus on the terms of the ceasefire monitoring mission, according to Reuters. The Syrian government have agreed to the protocol on the deployment of more observers.
A Syrian activist group has said clashes between troops and army defectors in an eastern city have left at least one person dead today.
The Britain-based Syrian Observatory for Human Rights said the clashes in Deir el-Zour also wounded three civilians.