Syrian rebel first responder service says airstrike killed 5

Bashar al-Jaafari, Syrian chief negotiator and Ambassador of the Permanent Representative Mission of Syria to UN New York, speaks at a media briefing after a round of negotiations between the Syrian government and the UN Special Envoy of the Secretary-General for Syria Staffan de Mistura at the European headquarters of the United Nations in Geneva, Switzerland, Tuesday, April 26, 2016. (Salvatore Di Nolfi/Keystone via AP) (The Associated Press)

Bashar al-Jaafari, Syrian chief negotiator and Ambassador of the Permanent Representative Mission of Syria to UN New York, arrives for a media briefing after a round of negotiations between the Syrian government and the UN Special Envoy of the Secretary-General for Syria Staffan de Mistura at the European headquarters of the United Nations in Geneva, Switzerland, Tuesday, April 26, 2016. (Salvatore Di Nolfi/Keystone via AP) (The Associated Press)

A video camera screen shows Bashar al-Jaafari, Syrian chief negotiator and Ambassador of the Permanent Representative Mission of Syria to UN New York, speaking at a media briefing after a round of negotiations between the Syrian government and the UN Special Envoy of the Secretary-General for Syria Staffan de Mistura at the European headquarters of the United Nations in Geneva, Switzerland, Tuesday, April 26, 2016. (Salvatore Di Nolfi/Keystone via AP) (The Associated Press)

A Syrian rebel-run first responder service says an airstrike has hit its training center in northern Syria, killing five personnel.

The Syrian Civil Defense, which conducts search and rescue operations in rebel-held areas, says the attack took place in the town of Atareb, west of the city of Aleppo, on Tuesday morning.

The organization called the attack a "massacre," on its social media pages.

The organization, also known as the White Helmets, has received global praise for its rescue operations in Syria.

The Britain-based activist group Syrian Observatory for Human Rights has confirmed the strike. The Observatory, a monitoring group that relies on a network of activists inside Syria, also reported that separately from the attack on White Helmets, pro-government forces also launched two rockets into Atareb on Tuesday.