Syrian troops bombarded the Damascus neighbourhood of Qabun on Friday as they pressed a bid to drive rebels out of the district, a watchdog said.
"Regime troops renewed shelling this morning of the Qabun neighbourhood and fierce clashes were underway between soldiers and rebels on the outskirts of the area," the Syrian Observatory for Human Rights said.
"Regime forces are hitting the area with mortar rounds, tanks and heavy artillery," the group added.
The fighting came on the third day of an attempt to clear rebels from the neighbourhood in northeastern Damascus, one of several districts where opposition forces have a foothold.
The clashes killed at least one rebel, and there were reports of deaths among troops as well, the Observatory said.
An explosion shook the neighbourhood around midnight (2100 GMT Thursday), the Observatory added, but it was unclear what had caused the blast and there was no word on any casualties or damage.
In the northern city of Aleppo, regime forces shelled districts, including the northern Sheikh Maqsud neighbourhood, and clashes left at least two rebels dead in the central Sulayman al-Halabi district.
Meanwhile, state television reported that the army had killed "several terrorists (rebels) around the Aleppo central prison, and destroyed anti-aircraft guns as well as weapons caches."
State media also carried denials from officials that there was a shortage of medicine in the prison, where the Observatory has said more than 100 deaths since April.
"All medications are available and in sufficient quantities inside the prison, and there is no one in danger of death because of a shortage of medicine," one official said, in remarks carried by SANA news agency.
Rebels fighting to topple Syrian President Bashar al-Assad, are trying to set free 4,000 detainees held in the prison.
In April they managed to seize part of the jail but the army still controls the buildings where the prisoners are kept. Troops and armed militants clash daily in and around the prison.