The British co- founder of an organization that trained the Syrian White Helmets civil defense group has been found dead in Istanbul on Monday, sources said.

"A comprehensive administrative and criminal investigation on the death of English citizen James Gustaf Edward Le Mesurier has been opened," the Istanbul governor's office said in an official statement.

Maria Zakharova, a Russian foreign ministry spokeswoman, accused Le Mesurier of being as a former agent of Britain’s MI6 last week.

"The White Helmets’ co-founder, James Le Mesurier, is a former agent of Britain’s MI6, who has been spotted all around the world, including in the Balkans and the Middle East. His connections to terrorist groups were reported back during his mission in Kosovo," Zakharova said in a statement on Twitter last week.

"We have learned with shock and sadness the news of the death of James Le Mesurier, founder and director of the humanitarian organization, May Day, early on Monday at his home in Tophane in Istanbul, Turkey. Mayday is one of the institutions supporting the White Helmets," White Helmets said in a statement on Twitter, confirming Le Mesurier's death. (ILKHA)