Syrian troops killed three people in the city of Homs on Thursday, a human rights group said, just one day after Damascus pledged to withdraw its forces from protest centres under an Arab League plan to end the bloodshed.
Activists called for mass demonstrations to test the genuineness of the government's commitment to the peace blueprint, voicing scepticism about its readiness to rein in a crackdown that the UN says has cost more than 3,000 lives since mid-March.
London and Washington said that despite Damascus's agreement to the Arab League plan after weeks of prevarication, they still believed President Bashar al-Assad must heed the demands of anti-government protesters and step down.
Under the deal announced at a meeting of Arab foreign ministers in Cairo on Wednesday, the Syrian government is supposed to withdraw its troops from all protest centres, although the text set no timetable.
The blueprint agreed by Syria, a copy of which was obtained by AFP, provides for a "complete halt to the violence to protect civilians."
It calls for the "release of people detained as a result of the recent events, the withdrawal of forces from towns and districts where there have been armed clashes, and the granting of access to the Arab League, and Arab and international media."
UN chief Ban Ki-moon said it was vital that Assad's regime now swiftly implement the Arab League plan in full.