Syrian tanks mounted with machine-guns fired Thursday on a city at the heart of the country's uprising, killing at least four people 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 a crisis that has endured for nearly eight months already with no sign of stopping despite a government crackdown that the U.N. 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 Thursday. 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.