Syrian forces shot dead at least four civilians on Sunday in a continued military assault on the central city of Homs and in an attack on pro-democracy demonstrations that erupted after prayers marking the main Muslim feast, an activist group said.

Three of the deaths occurred in Homs, 140 km north of Damascus, where a main district has been under tank bombardment since Tuesday. One demonstrator was shot dead when security police fired at a protest demanding the removal of President Bashar al-Assad in the city of Hama to the north, the Syrian Revolution General Commission (SRGC) said.

The organisation said in a statement that at least 10 protesters were also injured in the town of Talbisah near Homs and in Harra in the southern Hauran Plain.

Fifty protesters were arrested after a demonstration in the Damascus district of Kfrar Souseh. Troops deployed in several Damascus suburbs, surrounding mosques to prevent crowds from rallying after the early morning prayers for the feast of Eid al-Adha, it said.

Syrian authorities have banned most non-official media since an uprising against Assad's rule erupted seven months ago, making independent verification of events hard.

Officials say the unrest is largely a result of a foreign conspiracy to divide Syria and that security forces are using legitimate means to confront terrorists and Islamist militants bent on wrecking a reform drive by Assad.

Activists and residents said tank fire killed at least 13 civilians and wounded dozens in Homs on Saturday, casting doubt on whether an Arab League plan can end the bloodshed touched off by the popular uprising.

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

(Reporting by Khaled Yacoub Oweis, Amman newsroom; Editing by Mark Trevelyan)