A Ukrainian national has been arrested in western Germany on suspicion of spying for a Russian intelligence service, prosecutors said on Monday.

According to the Federal Public Prosecutor's Office, the 53-year-old is alleged to have gathered information on behalf of Russian intelligence about a man in Germany who took part in combat operations with the Ukrainian military following Russia's invasion of Ukraine in February 2022.

The Ukrainian man was detained in Hagen, south of Dortmund, on Friday and was remanded in custody on Saturday.

"The surveillance operation was presumably also intended to lay the groundwork for further intelligence operations against the target in Germany," prosecutors said.

German intelligence agencies have warned of the increasing threat posed by Russian espionage, sabotage and disinformation since Moscow's invasion of Ukraine.

With traditional intelligence operations involving professional spies having become more difficult due to sanctions and the increased vigilance of Western authorities, Russian actors have been accused of recruiting individuals from the petty criminal underworld for espionage or sabotage operations in return for payment.

Last week, a Ukrainian man was detained in Spain and a Romanian woman held in Germany over allegations of spying on a man in Germany who supplied drones and related components to Ukraine.

The two cases are not related, prosecutors said.