Tank fire has killed at least five civilians and wounded dozens in the besieged Syrian city of Homs, casting doubt on whether an Arab League plan can end months of bloodshed triggered by a popular uprising.

In Cairo, the Arab League chief said the organisation was seriously concerned by ongoing violence and appealed to Damascus to abide by steps agreed with Arab states to protect civilians and set Syria on the course of dialogue.

The civilian deaths in Homs, on the eve of the Muslim feast of Eid al-Adha, brought the death toll in the city since Tuesday, to at least 82.

Syrian authorities say security forces are fighting militant gangs who have been killing civilians and prominent figures in Homs.