VIENNA (Reuters) - Austrian prosecutors said on Friday they have charged a retired army colonel with spying and betraying state and military secrets, alleging that he worked for Russian military intelligence for at least 25 years.

The now 71-year-old former officer was arrested a year ago when spying allegations against him were first made public, embarrassing the then right-wing government that had positioned Austria as arguably Moscow’s closest ally in the European Union.

In a statement outlining the charges against him, the prosecutors’ office and police in his home province of Salzburg outlined what is believed to be his lengthy career as a spy and some of the elaborate communication methods involved.

From 1993 onwards, the officer provided “comprehensive information from the military spectrum of the Austrian Armed Forces, particularly on weapons systems and the assignment of tasks of ground and air forces”, the statement said.

In the course of his career as a spy for Russian GRU military intelligence, with which he first came into contact during a foreign assignment in 1987, he was paid hundreds of thousands of euros, the statement said, without naming him.

He continued to work for the GRU even after he retired, it said, adding that his last contact with his handler was in September 2018.

The statement provided few details on his activities but said he was part of a structured spy network that involved “painstaking documentation” of the information he provided.

“In addition to agent-management radio, the Internet using their own software, and highly complex satellite communication for transnational espionage activities, the armed forces spy and his Russian commanding officer also used additional modern spying technologies that required regular training of the defendant and corresponding instruction by the commanding officer,” the statement said.

Investigations into the handler are continuing, the statement said. It is not yet clear when the retired officer’s trial will begin.

Russia has denied knowledge of the Austrian officer and said the spying allegations are based on suspicions rather than evidence. The case follows other spying allegations against Russia that have soured relations with the European Union.

Neutral Austria was in the minority of EU countries that did not expel any Russian diplomats over the poisoning of former spy Sergei Skripal and his daughter in Britain, which London has blamed on Moscow. Russia denies any involvement.