Activists say Syrian government forces are battling rebels outside the capital Damascus and in Aleppo, where fighting for control over the country's largest city has raged for more than two weeks.

The activists group Syrian Observatory for Human Rights says residents have reported hearing loud blasts in Damascus on Friday from the shelling on the outer edges of the city.

Syrian troops say they have purged rebels from the capital after intense, week-long battles last month. But rebels continue to stage hit-and-run attacks and are active in the suburbs around the city.

Shelling and clashes are also continuing in the northern city Aleppo on Friday. The rebels said on Thursday they were low on ammunition but were still managing to put up resistance against a regime ground offensive there.