More than 100 people have been killed and others wounded by "barrel bombs" dropped by Syrian army helicopters on Aleppo that continued for a third day on Tuesday, Medecins Sans Frontieres MSF (Doctors Without Borders) said.
The casualties have overwhelmed the already overstretched and often-damaged hospitals in the northern city, where MSF is providing medical supplies, the aid group said.
"For the past three days, the helicopters have been targeting different areas, among them a school and the Haydarya roundabout, where people wait for public transport vehicles," said Aitor Zabalgogeazkoa, MSF coordinator in Syria.
"Repeated attacks often lead to chaos and make it more difficult to treat the wounded, therefore increasing the number of fatalities," he said in a statement.
President Bashar al-Assad's forces frequently deploy air power and artillery against rebel-held districts across Syria. They have been unable to recapture eastern and central parts of Aleppo, which rebels stormed in the summer of 2012, but they have driven rebel fighters back from towns to the southeast of the city in recent weeks.
The Syrian Observatory for Human Rights, which on Monday said 76 people had been killed by barrel bombs in Aleppo on Sunday, said 15 people, including two children, died in air raids by fighter jets on Aleppo's Shaar district on Tuesday.
The Britain-based group did not say whether they were caused by barrel bombs, which are explosive-filled cylinders or oil barrels, often rolled out of the back of helicopters, that are capable of causing widespread casualties and significant damage.
Helicopters dropped barrel bombs near the town of Safira, southeast of Aleppo, the Observatory said, but it was not clear whether there were any casualties.
Rebel fighters fired rockets at two Shi'ite towns near Aleppo city on Tuesday, the group said, delivering on a warning on Monday that they would target the towns if the bombing of Aleppo continued. It said there were no immediate details of casualties from the rocket fire.
More than 100,000 people have been killed in Syria since a revolt against President Bashar al-Assad began in March 2011, according to the latest U.N. death toll issued in July.