Overnight airstrikes in Aleppo have killed at least 61 people in 24 hours, Syrian activists say, including at least 27 people working at a hospital supported by Doctors Without Borders. Among the casualties were six hospital staff and three children, the Associated Press reports.

The hospital, Doctors Without Borders (also known by its French acronym MSF, for Médecins Sans Frontières), wrote on Twitter, was “well known locally & hit by direct airstrike on Wednesday.”

At least 186 people have been killed in a wave of violence that has passed over Aleppo since Friday, according to Agence France-Presse.

Rebel rocket and artillery fire on government-held neighbourhoods killed 18 civilians, the Syrian Observatory for Human Rights said.

Two children were among the dead, and about 40 people were wounded.

Regime air strikes on rebel-held districts, including the heavily populated Bustan al-Qasr neighbourhood, killed 20 civilians, including thre civilians, the Observatory said.

Mohammed Alloush, the chief Syrian opposition negotiator in the foundering Geneva peace talks, blamed the hospital attack on President Bashar Assad’s forces, describing them as one of his latest “war crimes.”

“Whoever carries out these massacres needs a war tribunal and a court of justice to be tried for his crimes. He does not need a negotiating table,” Alloush told the AP. “Now, the environment is not conducive for any political action.”