Two air strikes and at least one rocket attack staged overnight against an opposition-held area west of Aleppo killed five rescue workers, who appeared to have been knowingly targeted, a monitoring group and colleagues nearby reported.

The raids hit a center for the Syrian Civil Defence, known as the “White Helmets”, in the town of Atareb, some 25 km (15 miles) west of Aleppo.

The recent weeks have witnessed grave escalation in fighting in Aleppo province, as a partial truce brokered the United States and Russia in February has all but collapsed.

The Civil Defence corps work as first responders in opposition-held territory where medical infrastructure has broken down.

“The targeting was very precise,” Radi Saad, a Civil Defence worker based in northwestern Syria, told Reuters via internet.

“They were in the center and ready to respond. When they heard warplanes in the area they did not think they would be the target.”

It was unclear whether Syrian or Russian warplanes had launched the raids, he said. There was no immediate comment from the Syrian government.

Another Civil Defence member, Ahmad Sheikho, said five rescue workers had died and two were seriously wounded. Ambulances and cars belonging to doctors were also damaged.

The Syrian Observatory for Human Rights, a British-based monitoring group, said at least five had been killed, confirming that the center appeared to have been deliberately targeted.

The observatory also reported government air strikes and rebel bombardments in Aleppo city killing dozens of people in the last few days.

In the past 24 hours, fighting in Aleppo has killed at least 30 people including at least eight children, the Observatory added.