Heavy fighting has preceded the dawn start of a proposed truce in Syria's 19-month civil war, activists said.

Battles were still in progress at daybreak today, the beginning of a four-day Muslim holiday that was to coincide with the ceasefire.

Mediator Lakhdar Brahimi proposed the truce. The Syrian regime accepted it but said it would respond to rebel attacks. Some rebel groups said they would abide by the ceasefire.

The Britain-based Syrian Observatory for Human Rights, which relies on a network of activists, said the latest clashes took place in the central province of Homs, in Deir el-Zour in the country's east and in the city of Aleppo.

At least four rebels were killed and six soldiers were wounded in overnight fighting, the Observatory said.