BEIRUT — Activists say rebels are attacking several security compounds in the northern Syrian city of Aleppo.

The Britain-based Syrian Observatory for Human Rights said one of Friday's attacks targeted a compound in the neighborhood of Zahraa, killing and wounding a number of troops. It gave no figures.

Aleppo-based activist Mohammed Saeed said rebels are attacking four security buildings around Syria's largest city, using rocket launchers and machine guns.

Rebels took parts of Aleppo, Syria's commercial capital, last month. Since then, government forces have been trying to recapture them.

Activists estimate more than 20,000 people have been killed since the uprising against President Bashar Assad's regime began more than 17 months ago, turning into a civil war.

There has been fighting all over the country, including the capital, Damascus.