Two Syrian activist groups say they fear the past six days of clashes in two Damascus suburbs may have killed hundreds of people.

The Britain-based Syrian Observatory for Human Rights says the number of dead could be as high as 250.

Rami Abdul-Rahman, who heads the Observatory, says the group has documented 80 names of those killed in Jdaidet Artouz and Jdaidet al-Fadel suburbs.

The Local Coordination Committees, another activist group, says the death toll is 483. It says most of the people were killed in Jdaidet Artouz.

State-run news agency SANA said Syrian troops "inflicted heavy losses" on the rebels in the suburbs.

Monday's reports came as President Bashar Assad's forces continued a major offensive in the suburbs against opposition fighters who were closing in on parts of Damascus.