BEIRUT: Syrian tanks mounted with machine-guns fired on a city at the heart of the country's uprising on Thursday, killing at least four people in one day after Damascus agreed to an Arab League plan calling on the government to pull the military out of cities, activists said.

The violence does not bode well for the success of the Arab League initiative to solve the crisis that has endured for nearly eight months already, with no sign of stopping, despite a government crackdown that the UN estimates has left some 3,000 people dead.

Rami Abdul-Rahman, head of the British-based Syrian Observatory for Human Rights, said the Baba Amr, district of Homs came under heavy fire on Thursday.

At least four people were killed in Homs, he said, citing witnesses in the city.

Syria has largely sealed off the country from foreign journalists and prevented independent reporting, making it difficult to confirm events on the ground.

Key sources of information are amateur videos posted online, witness accounts and details gathered by activist groups.

Under the Arab League plan announced on Wednesday, Damascus agreed to stop violence against protesters, to release all political prisoners and to begin a dialogue with the opposition within two weeks.

Syria also agreed to allow journalists, rights groups and Arab League representatives to monitor the situation in the country under the Arab League plan.

Najib al-Ghadban, a US-based Syrian activist and member of the opposition Syrian National Council, was skeptical that Syrian President Bashar Assad would hold up his end of the deal, and called the agreement ''an attempt to buy more time.''

''This regime is notorious for maneuvering and for giving promises and not implementing any of them,'' he said.

Syria blames the violence on ''armed gangs'' and extremists seeking to destabilise the regime in line with a foreign agenda, an assertion that raised questions about its willingness to cease all forms of violence.

Previous attempts to hold dialogue with the opposition were unsuccessful.

The Arab League initiative appears to reflect the group's eagerness to avoid seeing another Arab leader toppled violently and dragged through the streets, as was slain Libyan strongman Muammar Qadhafi last month.

An Arab League decision had paved the way for Nato air strikes that eventually brought down Qadhafi.