ISTANBUL — The British founder of a group that helped establish the Syrian White Helmets rescue organization has died in Istanbul, his office said on Monday.

The precise details of James Le Mesurier's death could not be confirmed and his office did not wish to comment further.

Le Mesurier was a former British Army officer who founded Mayday Rescue, which helped train the White Helmets when it began in 2013.

Local media reports said his body was found with fractures to his legs and head at the foot of his apartment early on Monday.

The Istanbul governor's office said an investigation would be launched into the death.

The White Helmets, officially known as Syria Civil Defense, expressed their "shock and sadness" on Twitter.

The voluntary search-and-rescue group was formed to respond to bombings by Syrian government forces in opposition-controlled parts of the country.

Le Mesurier said in 2015 in an interview that he had begun training and supporting the organization in early 2013 alongside Turkish rescue experts, starting with "a single team of 20 people".

"I was working in Istanbul... and got together with a group of Turkish earthquake rescue volunteers," he said.

The White Helmets quickly expanded, and are credited with saving tens of thousands of lives during Syria's conflict.

A documentary about the group won an Academy Award in 2017.

The White Helmets have become a favorite target of pro-Syrian and pro-Russian groups. They have accused the group of supporting terrorists in Syria and doctoring footage of atrocities committed by regime forces — claims strongly denied by its supporters.

Just three days ago, the Russian foreign ministry tweeted about Le Mesurier, describing him as "a former agent of Britain's MI6, who has been spotted all around the world, including in the #Balkans and the #MiddleEast.

"His connections to terrorist groups were reported back during his mission in #Kosovo." — AFP