At least 150 Syrian regime forces have been killed in Khan al-Assal, a town in Aleppo province at the centre of an alleged chemical weapons strike, monitors said Friday.
The Syrian Observatory for Human Rights also said that at least 10 people were reported killed in regime shelling of the northwestern province of Idlib.
Observatory director Rami Abdul Rahman also told AFP at least 10 people had been killed and 50 wounded, several critically, in a rocket attack on the Bab Nairab suburb of Aleppo city.
"Regime forces fired a surface-to-surface rocket that targeted a headquarters for several combat battalions including the Islamic State of Iraq and the Levant. It fell several tens of metres (yards) away onto civilian homes," the Observatory said.
The deaths in Khan al-Assal came as the regime tried to recapture the northern town, which fell to rebels on Monday.
More than 50 of those killed were executed by rebels after the town fell, with the rest having died in fighting, the Observatory said, adding that 30 of the dead were officers.
Rebels had for months tried to take Khan al-Assal, a strategically located town in the west of Aleppo province. They finally seized it on Monday but fighting raged on its edges the next day, said the Observatory.
Amateur video filmed by rebels and distributed by the Observatory showed the bodies of dozens of regime forces in a building that had been the site of a battle.
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The mainstream rebel Ninth Division claimed its fighters took Khan al-Assal. But footage distributed by the Britain-based Observatory said jihadists including Al-Nusra Front were behind the takeover.
Fierce fighting raged in March in Khan al-Assal during eight days in which 200 rebels and government forces were killed.
Both sides have traded accusations that chemical weapons were used in Khan al-Assal and killed around 30 people, according to a toll released that month by the Observatory and the regime.
During a visit to Damascus by two UN envoys earlier this week, Syrian authorities reiterated their demand that the United Nations focus on investigating the alleged use of chemical weapons in Khan al-Assal.
Khan al-Assal's fall to rebels has complicated any effort to send in inspectors to visit the site.
At the United Nations on Friday, opposition Syrian National Coalition leader Ahmad Jarba called on the Security Council to apply greater "international pressure" on President Bashar al-Assad to halt the bitter conflict.
Elsewhere in Syria, the Observatory reported 10 people killed and several wounded in regime shelling of the Idlib village of Basamis.
Syria opposition activists also held small anti-regime protests in several towns across the country.
The Observatory, which relies on a vast network of activists on the ground and medics for its information, said at least 85 people were killed throughout Syria on Thursday -- 29 civilians, 32 rebels and 24 soldiers.