Investigators have arrested two German-Russian men on suspicion of spying for Russia and planning attacks in Germany -- including on US army targets -- to undermine military support for Ukraine, prosecutors said Thursday.

The pair, identified only as Dieter S. and Alexander J., were arrested in Bayreuth in the southeastern state of Bavaria on Wednesday, federal prosecutors said in a statement.

The main accused, Dieter S., is alleged to have scouted potential targets for attacks, "including facilities of the US armed forces" stationed in Germany.

Russia's ambassador to Berlin was summoned by the foreign ministry following the arrests.

Germany would not "allow Putin to bring his terror to Germany", Foreign Minister Annalena Baerbock subsequently said on X.

But Russian officials rejected the accusations.

"No evidence was presented to prove the detainees' plans or their possible connection to representatives of Russian structures," the Russian embassy in Berlin said in a post on X.

Police have searched both men's homes and places of work.

They are suspected of "having been active for a foreign intelligence service" in what prosecutors described as a "particularly serious case" of espionage.

Interior Minister Nancy Faeser likewise called the allegations "a particularly serious case of suspected agent activity for (Vladimir) Putin's criminal regime".

"We will continue to thwart such threat plans," she said, reiterating Germany's steadfast support for Ukraine.