The trial of a retired Austrian army colonel accused of spying and betraying state and military secrets to Russian military intelligence for at least 25 years has started in Salzburg.

The former officer, 71, was arrested in November 2018 and charged last November, with prosecutors accusing him of having passed on secret information about the Austrian military’s weapons systems and artillery positions in exchange for about €280,000 (£243,000).

Judges at Salzburg’s regional court announced on Monday morning that the trial would be held behind closed doors since evidence raised was likely to include state secrets and military intelligence.

The retired colonel, from Salzburg, denies all the allegations, claiming to have merely passed on information that was already public in newspapers or on the internet. His lawyer said his client was “a patriot” who kept in touch with “certain persons abroad” but never breached the law in doing so.

Investigations by Austria’s Office for the Protection of the Constitution and Counterterrorism revealed that the accused first contacted Russia’s military intelligence agency, the GRU, during a foreign assignment in 1987.

In July 2019 Austria issued an international arrest warrant for a Russian military officer, Igor Egorovich Zaytsev, who they say recruited the colonel. European and international warrants have been issued for him at the request of the Salzburg police.

According to Austrian media, the colonel kept in touch with his Russian handler using sophisticated equipment.

The trial, which will hear from 19 witnesses, is scheduled to last for five court days, with a verdict expected on 19 March.