State-owned RIA said David Orrells, who worked as a drone operator for the Organisation for Security and Cooperation in Europe (OSCE), was suspected of handing over intelligence on the positions of Russian-backed fighters and weaponry that the Ukrainians then used to launch attacks on them.
Contacted by Reuters, Orrells said he had left Ukraine's Luhansk region in February last year, shortly before Russia invaded Ukraine, and was now "perfectly safe" back in the UK.
He described the allegation as "laughable" and said he did not know why it was being made now.
The investigation was launched by the state security ministry of the Lugansk People's Republic (LPR), one of Russia's proxies in the Donbas region of eastern Ukraine.
Before the invasion, Orrells led an OSCE team using drones to monitor a frequently violated ceasefire between Ukrainian troops and Russian-backed forces, in a conflict that had dragged on since 2014.
He said he passed on the images for analysis by OSCE colleagues who filed daily updates on the situation along the line of contact between the two sides.
Orrells said the monitors encountered "massive suspicion" from the LPR side. "They would do anything to upset and annoy and obstruct us."
The OSCE ended the mission after the Russian invasion on Feb. 24 last year.
(Reporting by Mark Trevelyan, Editing by William Maclean)
By Mark Trevelyan
