Children were among an estimated 18 people killed today when a Syrian warplane bombed a building in the rebel town of Al-Bab, in Aleppo province, Agence France Presse reported.
The London-based Syrian Observatory for Human Rights told AFP at least 10 men, six women and a young girl and boy died when the fighter jet blew up the building where they were sheltered.
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An activist network inside Syria, the Syrian Revolution General Commission, said the death toll was expected to rise, with victims still stuck in the rubble, the Australian Associated Press reported.
The activists said ongoing aerial attacks in the vicinity were making rescue attempts impossible.
According to the BBC, Al-Bab, which is north-east of Aleppo city, has been “heavily pounded” by regime forces in recent weeks.
Activists say the Syrian government has been targeting towns and villages in the Aleppo countryside in an effort to break rebel supply lines into the city.
Following today's strikes on Al-Bab, the state news agency SANA reported that the the army had "seized large quantities of arms and ammunition" from the rebels on the outskirts of Aleppo city.
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In separate fighting, the Syrian Observatory for Human Rights said rebels were mounting new offensives in both in the capital Damascus; and the north-western province of Idlib, after being pushed back by regime forces, AFP reported.
In an interview with the BBC in New York, Lakhdar Brahimi, the new international envoy to Syria, said he viewed his mission as near-impossible.
"I'm coming into this job with my eyes open, and no illusions ... I know how difficult it is,” he said.
Brahimi said he had no firm peace plan for Syria, and would keep the six-point peace plan of his predecessor, Kofi Annan, in his "tool box" for possible adaptation, the BBC reported.
Brahimi is expected to meet President Bashar al-Assad in Syria on Saturday.