Syrian troops killed seven people in the flashpoint central 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.

The seven people on Thursday died in the Baba Amr and Al-Inshaat neighbourhoods of Homs, the Syrian Observatory for Human Rights said.

"Heavy machinegun fire is still being heard," the Britain-based watchdog added in a statement received in Nicosia.

Under the hard-won deal announced at a meeting of Arab foreign ministers in Cairo late 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."

It also stipulates that "the Arab ministerial committee (headed by the prime minister of Qatar) will conduct consultations with the government and the various Syrian opposition parties aimed at launching a national dialogue."

The text did not specify a venue for the dialogue, a bone of contention between the government, which insists on Damascus, and the opposition which says it should be outside Syria.

The Local Coordination Committees (LCC), which organised the anti-government protests on the ground, said it doubted "the integrity of the Syrian regime's acceptance of the points suggested by the Arab League's initiative."

It called on Syrians to "validate whether armed forces... have been withdrawn from the cities and towns, and whether violence has been stopped, detainees have been released, Arab and international media correspondents have been allowed in the country, and if a dialogue has been made possible."

"This validation should come through maintaining all forms of peaceful protest," it said.

"May tomorrow, Friday, be the day where all streets and squares become platforms for demonstrations and for the peaceful struggle towards achieving the downfall of the regime."

UN chief Ban Ki-moon said it was vital that Assad's regime now swiftly implement the Arab League plan in full.

"He must implement the agreement as soon as possible as agreed," Ban told a news conference in Tripoli on Wednesday.

Qatari Prime Minister Sheikh Hamad bin Jassem al-Thani, who led the Arab League's mediation efforts, said "if Syria does not respect its commitments, the ministerial committee will meet again and take the necessary decisions."

British Foreign Secretary William Hague too called on the Syrian government to stand by its undertakings under the peace plan.

"As the Arab League has made clear, it is vital that the plan is implemented quickly and fully," he said.

Hague stressed however that Britain continued to believe that the only real way to end the bloodshed was for Assad to go.

"We continue to believe that President Assad should step aside and allow the Syrian people to realise their aspirations for greater freedom, dignity and a more open political system," he said.

It was a position echoed by Washington. "Our position remains that President Assad has lost his legitimacy to rule and should step down," White House spokesman Jay Carney said.

China, which had pressed Syria to accept the Arab League plan after vetoing a Western-drafted resolution at the UN Security Council early last month that threatened targeted measures against the regime, welcomed Wednesday's deal.

"We hope all parties concerned in Syria can make practical efforts to stop all violence and create conditions for solving the relevant issues through dialogue and consultations," foreign ministry spokesman Hong Lei told reporters.

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