Khaled Omar Harrah, a volunteer rescuer who spent nearly three years rushing to the scenes of airstrikes and barrel bombs to save lives, has been killed in the embattled city of Aleppo.

The Syrian Civil Defense Force, also known as the White Helmets, tweeted remembrances of Harrah, calling him a "true hero" who saved "countless lives." A spokesman for the search-and-rescue group told CNN that he was killed during an airstrike, and was "with other members of his team helping people trapped in rubble."

Harrah was a painter and decorator before the start of the war.

He became one of the most prominent faces of the White Helmets when he saved a 10-day-old baby from the rubble of a collapsed building in 2014. The moment became known as the "miracle baby" rescue, after the scene was caught on camera and went viral. The video shows Harrah brushing aside debris and reaching through a hole in the wall to gently pull the child out, as the gathered crowd cheers.

You can watch it here:

The moment came some 16 hours after the rescue operation started, he said while recounting the event at the United States Institute of Peace in 2014. Three families lived in the building, which was struck by a bomb, and the White Helmets had rescued a number of people after hours of digging.

They were packing up to leave when a woman approached them and said that her two children were still missing — a year-and-a-half-old daughter, and a 10-day-old son. In an interview with Vocativ , Harrah described how the mother wasn't completely sure which section of the house the baby, named Mahmud, was trapped in:

"She led them to one section of the flattened house. 'My baby is here!' she cried. But Mahmud was nowhere to be found. The mother led them to another area, but the rescuers couldn't find anyone there, either. 'Every time it was a different place,' says Harrah. 'She couldn't remember.'"By 3:30 p.m., some nine hours after the bombing, Harrah lied down to rest, his ear resting against the concrete, when suddenly he heard a baby crying beneath him. 'I thought I was being delusional because I was so tired. I asked my friend, 'Will you listen? Put your ear here and try to hear. I think I hear a baby's voice.' He said, 'Yes, it is!' "

Hours later, baby Mahmud was free — and survived the ordeal. Vocativ said that when Harrah saw Mahmud after the rescue, the child fell asleep in his arms. Harrah said, "If I die saving lives, I think God would definitely consider me a martyr."

This is just one story of many. A tribute from the Syria Campaign , an advocacy group, said that Harrah was "one of the earliest volunteers of the White Helmets" who has "responded to thousands of attacks." It said he has a wife and two young daughters.

As NPR has reported , the White Helmets have "been responsible for saving more than 40,000 lives." The group's head Raed Al Saleh told NPR that the volunteers "do whatever they can to get to people and transport them to hospitals while they're alive. ... They treat survivors equally and do the most thorough job they can."

The White Helmets function as Aleppo's emergency service. "These bombings and attacks don't exclude any side, they bomb all civilians and institutions," Dr. Osama Abo El Ezz, a surgeon from the city, told Weekend Edition . "On a daily basis, we receive scores of martyrs and hundreds of injured people who are being brought to the medical institutions."

Copyright 2016 NPR. To see more, visit http://www.npr.org/ .