Syria's army and rebels were preparing Friday for a major battle for control of strategic airports in Aleppo, a watchdog said, four days after insurgents launched assaults on airbases in the northern province.
The Syrian Observatory for Human Rights said intermittent clashes were reported around Aleppo international airport, Nayrab airbase and another military complex as the two sides squared up for a major fight.
"The army shelled the area around Aleppo international airport and Nayrab air base on Friday morning, while rebels used home-made rockets to shell Nayrab," Observatory director Rami Abdel Rahman said.
"The army is preparing a large-scale operation to take back control of Base 80," he added of a military complex tasked with managing both Nayrab and Aleppo airports.
Rebels seized the base on Wednesday after a battle that left at least 150 dead from both sides, among them senior army officers, said the Observatory.
Insurgents fighting President Bashar al-Assad's regime "are trying to take control of Nayrab and to destroy the runways at Aleppo international airport, which the army is using for military purposes," Abdel Rahman said.
Activists in Aleppo have said the rebel Free Syrian Army shifted its focus weeks ago from the city to airbases in the province.
Insurgents see the capture of airports such as Al-Jarrah, also in Aleppo province, on Tuesday as a way of seizing large amounts of ammunition and to put out of action warplanes used by the regime to bombard rebel-held areas.
Regime tanks, meanwhile, shelled the town of Khan Sheikhun in the province of Idlib, killing at least 11 civilians, said the Observatory.
In Damascus, the army shelled the eastern district of Jobar, where rebels have set up enclaves, the Britain-based group said.
Friday's violence came a day after at least 155 people were killed across Syria, it said.
Meanwhile, anti-regime protesters took to the streets in flashpoints including Daraa in the south, Deir Ezzor near the Iraqi border, Homs in the centre and Aleppo in the north.
Amateur videos distributed by activists and the Observatory showed that protesters renewed calls for the fall of Assad's regime, as they have every Friday since the outbreak of the revolt in March 2011.
"We prefer to die than to be humiliated!" chanted protesters in Kafr Zita, a town in the central province of Hama that has been the target of regular regime bombardment.
"In spite of you, O Bashar, we have our freedom!" chanted protesters in Sukkari, a rebel-held district of Aleppo.