Syrian troops bombed southern districts of Damascus on Friday while rebels and soldiers battled around two military schools in the north of the country, the Syrian Observatory for Human Rights said.
"Several blasts rang out in Damascus as southern areas of the city were bombarded," said the Britain-based group.
Nine rebels and eight soldiers were killed in heavy clashes near the School of Administrative Affairs, a military academy between Aleppo city and the town of Saraqeb to the southwest.
"Classes were suspended there several months ago after rebels seized much of the surrounding area," Observatory director Rami Abdel Rahman told AFP.
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Just north of Aleppo, fighting broke out near another military academy, one of the largest in the country, said the watchdog, which relies on a countrywide network of activists and doctors in compiling its reports.
The insurgents, who have encircled the sprawling infantry school for three weeks, will nevertheless have to mobilise significant numbers of fighters to take on the 3,000 soldiers stationed there, Abdel Rahman said.
In the Tassil area of the southern province of Daraa, three civilians were killed and several wounded by artillery fire at dawn, the watchdog said.
Fighting also broke out in the northwestern province of Idlib around the military base at Wadi Daif, under siege by rebels since they seized the nearby town of Maaret al-Numan, which was hit by air raids on Friday.
The Observatory said at least 42 people -- 14 civilians, 20 rebels and eight soldiers -- had been killed nationwide on Friday.