BEIRUT: Southern Damascus saw fresh clashes early on Friday, as army tanks battered rebel enclaves near the Syrian capital, a monitoring group said.

In northern Syria, unidentified gunmen opened fire on a bus in Aleppo province, killing four civilians, among them three university students, said the Syrian Observatory for Human Rights

"Fresh clashes broke out near Yarmuk camp... while the area was shelled," said the Observatory, which relies on a broad network of activists, lawyers and doctors for its reporting.

Violence at Yarmuk, once home to some 150,000 Palestinian refugees living in Syria, has raged for several weeks, forcing many onetime residents to flee from the area.

"Yarmuk was not only home to Palestinians, but also to many Syrians fleeing violence elsewhere," an anti-regime activist from Damascus who identified himself as Abu Yasser told AFP.

"Now, they have no safe place to go to any more in the capital," he said, adding his family was also forced to flee southern Damascus.

Near the capital, tanks shelled several insurgent-held areas, among them Yabrud, Irbin, Moadamiyet al-Sham and Yalda, said the Observatory.

Since the end of summer last year, the army has waged a fierce onslaught on rebel enclaves near Damascus in a bid to stop insurgents from approaching the capital.

In Aleppo province, army shelling hit the town of Sfeira after clashes pitting troops against jihadist fighters loyal to Al-Nusra Front in the area on Thursday night, during which five soldiers where killed, said the monitoring group.

The city of Homs in central Syria was also pounded on Friday morning, more than six months into a suffocating army siege on several rebel-held districts, the activists said.

"The district of Khaldiyeh was shelled by army tanks on Friday morning, as several explosions shook the area," said the Observatory.

Violence across Syria has killed more than 60,000 people in 22 months, the UN says.