(Bloomberg) -- German authorities arrested two men suspected of spying for Russia and membership of a terror group planning acts of sabotage, in a case the interior minister called “particularly serious.”

The Federal Prosecutor General in Karlsruhe named the pair of German-Russian citizens as Dieter S. and Alexander J. and said the alleged members of a pro-Kremlin group known as the “Donetsk People’s Republic” were taken into custody Wednesday in the Bavarian city of Bayreuth.

Dieter S. had been in contact with an individual connected to a Russian intelligence service since October last year about “possible sabotage actions” against military and industrial sites in Germany, including US installations, the Prosecutor General said Thursday in an emailed statement.

“Against this background, the accused declared to his interlocutor that he was prepared to carry out explosive and arson attacks,” it said, adding that the intention was “in particular to undermine the military support provided from Germany to Ukraine.”

The arrests are the latest evidence of apparent Russian spying in Germany, a phenomenon that strained relations between Berlin and Moscow even before President Vladimir Putin ordered a full-scale invasion of Ukraine in February 2022.

German Foreign Minister Annalena Baerbock summoned the Russian ambassador in Berlin to her ministry to discuss the case.

“It’s an extremely serious suspicion that Putin is recruiting agents in our country to carry out attacks on German soil,” Baerbock wrote on X. “We will not allow Putin to bring his terror to Germany. This was communicated to the Russian ambassador today during a summons.”

The Russian embassy said in a statement the claims were a “provocation aimed at inciting the already rampant spy mania in Germany.”

In August 2019, a former Chechen military commander was gunned down in broad daylight in a central Berlin park, a killing a court later found was ordered by Moscow, while two men are currently on trial suspected of passing classified material from the BND foreign intelligence service to the Kremlin.

Next month, a trial will get underway in Stuttgart in which a man and a woman are charged with delivering electronic parts to Russia that are being used in drones deployed in the war on Ukraine, allegedly violating a European Union embargo.

Interior Minister Nancy Faeser said Thursday Germany won’t allow itself to be “intimidated” by Russia and will “continue to provide the government in Kyiv with massive support.”

“Since Russia’s murderous war of aggression against Ukraine, our security authorities have ramped up all protective measures against hybrid threats from the Russian regime,” Faeser said in an emailed statement. “Now we must continue to clarify all the background and connections.”

The Prosecutor General also mentioned “strong suspicion” that Dieter S. was active in eastern Ukraine between late 2014 and September 2016 as a fighter in an armed unit of the “Donetsk People’s Republic.”

In Germany, he “scouted out some of the targeted objects on site, taking photos and videos, for example of military transports and goods,” and “passed on the information he gathered to his interlocutor,” according to the statement.

--With assistance from Karin Matussek, Arne Delfs, Michael Nienaber and Dina Khrennikova.

(Updates with Baerbock comment in the seventh paragraph)

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