Almost 2,000 people have been killed by Syrian government air attacks in the northern city of Aleppo so far this year, an activist group says.
The dead included 283 women and 567 children, according to the Syrian Observatory for Human Rights (SOHR).
The Syrian air force has used so-called "barrel bombs" dropped from aircraft to try to put down a rebellion against President Bashar al-Assad.
Aleppo has seen fierce fighting since a rebel offensive in the area in 2012.
The UK-based SOHR said 1,963 people had been killed in the city - Syria's largest - and the surrounding area since January.
The government has used air and ground forces to drive the rebels back, but they remain in control of some areas to the east of Aleppo.
The SOHR - which has a network of activists around the country reporting on the violence - says more than 162,000 people have been killed in the three-year conflict.
Analysis: Jim Muir, BBC News, Beirut
The barrels, packed with explosives, are a crude weapon, rolled out of helicopters, often from high altitude.
They're extremely inaccurate; they cause a huge blast and massive damage, often devastating entire quarters in the densely-built-up areas of Aleppo controlled by rebel forces.
Underlining the complexity of the conflict now going on in Syria, the Syrian observatory has also reported that 15 Kurdish civilians, including seven children and three women, were summarily executed by fighters from the extremist Islamic State in Iraq and the Levant (ISIS), after they overran a village in the north-east of the country.
The use of shrapnel-packed barrel bombs in Aleppo and elsewhere has been condemned by international human rights groups.
The bombs are dropped from helicopters and cannot be guided or controlled.A BBC team witnessed the effects of the weapons on Syrian civilians in rebel-held areas of Aleppo in April.
Last week government forces broke a year-long rebel siege of Aleppo's central prison.
Correspondents say the government breakthrough has cut off a major supply route for the rebels from Turkey.