A former British army officer, who helped start the “White Helmets”, an emergency response group in Syria, has been found dead near his home in Istanbul, just days after the Russian foreign ministry menaced him, accusing him of being a spy.

James Le Mesurier, 48, was the director of Mayday Rescue charity that trained members of the Syria Civil Defence, nicknamed the White Helmets, playing a major role in its creation in Turkey in 2013.

He was awarded an OBE for his work helping Syrians three years later.

The police have yet to confirm how Mr Le Mesurier died, but he is believed to have fallen from the balcony of his apartment in the Turkish city at dawn on Monday.

His death comes just three days after he was publicly attacked by Maria Zakharova, Russia’s foreign ministry spokeswoman, who on Friday claimed he was a “former agent of Britain’s MI6, who has been spotted all around the world”.

He and the White Helmets had been the subject of a disinformation campaign spearheaded by Moscow and their allies in Damascus for years.

The White Helmets assist in Douma, Syria Show all 14 1 /14 The White Helmets assist in Douma, Syria The White Helmets assist in Douma, Syria Douma, the largest town in the Eastern Ghouta area with more than 100,000 residents, is surrounded and regularly shelled by regime forces EPA The White Helmets assist in Douma, Syria epaselect epa05635971 Volunteers of the Syrian Civil Defense, also known as the White Helmets, carry large pieces of burned wood as they try to extinguish a fire after a bombing in Douma, on the outskirts of Damascus, Syria, late 17 November 2016. According to local reports, at least six people were killed and 30 injured in several bombings mostly throughout the night. EPA/MOHAMMED BADRA EPA The White Helmets assist in Douma, Syria epaselect epa05636079 A volunteer of the Syrian Civil Defense, also known as the White Helmets, looks at a burning structure after a bombing in Douma, on the outskirts of Damascus, Syria, late 17 November 2016. According to local reports, at least six people were killed and 30 injured in several bombings mostly throughout the night. EPA/MOHAMMED BADRA EPA The White Helmets assist in Douma, Syria Members of the Syrian Civil Defense, known as the White Helmets, extinguish fire following a reported government airstrike on the rebel-held town of Douma, on the eastern outskirts of the capital Damascus, on November 17, 2016. Douma, the largest town in the Eastern Ghouta area with more than 100,000 residents, is surrounded and regularly shelled by regime forces. / AFP PHOTO / Sameer Al-DoumySAMEER AL-DOUMY/AFP/Getty Images Getty The White Helmets assist in Douma, Syria A Syrian man searches for victims as fire spreads following a reported government airstrike on the rebel-held town of Douma, on the eastern outskirts of the capital Damascus Getty The White Helmets assist in Douma, Syria Members of the Syrian Civil Defense, known as the White Helmets, extinguish fire following a reported government airstrike on the rebel-held town of Douma Getty The White Helmets assist in Douma, Syria Members of the Syrian Civil Defense, known as the White Helmets, extinguish a fire following a reported government airstrike on the rebel-held town of Douma, on the eastern outskirts of the capital Damascus Getty The White Helmets assist in Douma, Syria Syrians run for cover following a reported government airstrike on the rebel-held town of Douma, on the eastern outskirts of the capital Damascus Getty The White Helmets assist in Douma, Syria Members of the Syrian Civil Defense, known as the White Helmets, search for victims following a reported government airstrike on the rebel-held town of Douma, on the eastern outskirts of the capital Damascus, on November 17, 2016. Douma, the largest town in the Eastern Ghouta area with more than 100,000 residents, is surrounded and regularly shelled by regime forces. / AFP PHOTO / Sameer Al-DoumySAMEER AL-DOUMY/AFP/Getty Images Getty The White Helmets assist in Douma, Syria A Syrian man searches for victims following a reported government airstrike on the rebel-held town of Douma, on the eastern outskirts of the capital Damascus, on November 17, 2016. Douma, the largest town in the Eastern Ghouta area with more than 100,000 residents, is surrounded and regularly shelled by regime forces. / AFP PHOTO / Abd DoumanyABD DOUMANY/AFP/Getty Images Getty The White Helmets assist in Douma, Syria A member of the Syrian Arab Red Crescent searches for victims following a reported government airstrike on the rebel-held town of Douma, on the eastern outskirts of the capital Damascus, on November 17, 2016. Douma, the largest town in the Eastern Ghouta area with more than 100,000 residents, is surrounded and regularly shelled by regime forces. / AFP PHOTO / Abd DoumanyABD DOUMANY/AFP/Getty Images Getty The White Helmets assist in Douma, Syria Injured Syrian men receive treatment at a makeshift hospital following a reported government airstrike on the rebel-held town of Douma, on the eastern outskirts of the capital Damascus, on November 17, 2016. Douma, the largest town in the Eastern Ghouta area with more than 100,000 residents, is surrounded and regularly shelled by regime forces. / AFP PHOTO / Abd DoumanyABD DOUMANY/AFP/Getty Images Getty The White Helmets assist in Douma, Syria An injured Syrian man receives treatment at a makeshift hospital following a reported government airstrike on the rebel-held town of Douma Getty The White Helmets assist in Douma, Syria Injured Syrians receive treatment at a makeshift hospital following a reported government airstrike on the rebel-held town of Douma, on the eastern outskirts of the capital Damascus, on November 17, 2016. EPA

“We were informed by his family that he had died,” Raed al-Salah, the head of the White Helmets, told The Independent.

“We read that the police found his body outside his home in Istanbul. But as of now, the police are investigating the case and have drawn no conclusions yet. We are waiting for the police report,” he added.

“James is a close friend to us and to the Syrian people, he supported the White Helmets as founder and director of the Mayday Rescue organisation. We are devastated.”

A neighbour told Reuters Mr Le Mesurier, who leaves behind two children, was found dead early on Monday near his home in central Istanbul’s Beyoglu district. A diplomat said the circumstances around his death were unclear.

The Turkish state-run Anadolu news agency said that worshippers on their way to a mosque had found this body near his home. Anadolu added that police established that no one had entered or left his home at the time of the incident and believe he may have fallen to his death.

The Istanbul governor’s office said that “comprehensive administrative and judicial investigations into Mr Le Mesurier’s death have been initiated”.

Friday’s tweet from Maria Zakharova, Russia’s foreign ministry spokeswoman

The White Helmets have been credited with saving thousands of lives in rebel-held areas during years of bombing by Syrian government and Russian forces in the country’s civil war.

Mayday Rescue is a nonprofit organisation with offices in Amsterdam and Istanbul whose projects have been funded by the United Nations and various governments.

However Russia, which has been fighting alongside Syrian president Bashar al-Assad’s forces in the eight-year civil war, regards the White Helmets as a terrorist-linked organisation and has mounted a vicious campaign against the group.

During a regular press briefing on Friday, Russian spokeswoman Maria Zakharova personally attacked Mr Le Mesurier, claiming he had worked as a British spy across the world including the Balkans, and the Middle East as well as with members of al-Qaeda.

“The work James and the White Helmets did is phenomenal. There are few people who have done more on the humanitarian side,” said Hamish de Bretton-Gordon, a chemical weapons expert who served with Mr Le Mesurier in the army and was a friend.

“But like all of us he suffered from Russian and Syrian disinformation and propaganda. To claim he worked for MI6 and al-Qaeda is a contradiction and crass. He was an amazing army officer and humanitarian,” Mr de Bretton-Gordon added.

Ms Zakharova also claimed the White Helmets “stage provocations ... [and have] planned and carried out a series of ruthless fake chemical attacks” in her briefing

In the past Russian and Syrian officials have accused the White Helmets of “staging” airstrikes to frame Syrian or Russian forces.