The suspect has been identified as a Russian citizen who planned to kill one of Moscow’s critics in Warsaw.

Polish Prime Minister Donald Tusk has announced that a Russian citizen has been arrested over an alleged plot to kill an American citizen of Ukrainian origin in Warsaw.

In Thursday’s announcement, Tusk did not provide details about the plot or identify the alleged target.

He, however, said the citizen of the United States was considered “inconvenient to the Putin regime” and that Polish authorities arrested the suspect on August 7.

Tusk added that the plot marks the first known instance of “someone on the order of Russia” deciding to attack a US citizen on the territory of another NATO country. He called the incident a “very dangerous signal”, and he thanked Poland’s security services.

“At the last minute, thanks to the action of the Internal Security Agency and the police, we managed to prevent this execution, this attack,” Tusk said.

Experts have warned that the reported plot comes amid a rise in threats from Russia, which has been accused of killing critics abroad, including through contract killers and poisonings.

Since February 24, 2022, Russia has been locked in a full-scale war with Ukraine, after it launched an invasion that pushed towards the Ukrainian capital of Kyiv.

Russian President Vladimir Putin, however, has blamed the conflict in part on NATO, accusing the military alliance of seeking to extend its influence eastwards. NATO has supported Ukraine politically and with military aid, maintaining that the Eastern European country has the right to self-defence.

Still, the fallout from the war has been felt across the region. European countries have expressed increasing alarm over Russia’s aggressive posture, with Russian military planes repeatedly flying near NATO airspace.

Last week’s arrest comes after Poland and several Baltic states bordering Russia said they were watching threats from Moscow and had ramped up security at key infrastructure sites.

Earlier this month, German authorities also said they faced “a new level of danger” after finding a quadcopter drone laden with explosives near an airport. While officials have not identified Russia as a culprit, US intelligence reports suggest Moscow may have been operating the drone.

Lithuanian Defence Minister Robertas Kaunas also alleged last week that Moscow was planning “false flag” attacks on infrastructure in the region, using captured Ukrainian drones to “frame” Kyiv.

Russia has accused Ukraine of carrying out the killings of individuals linked to the country’s war efforts, pointing to an explosion that killed a Russian military officer in the annexed Ukrainian territory of Crimea on Thursday.

Authorities in several European countries, including France, Lithuania and Germany, have broken up plots allegedly attempting to target Russian dissidents and individuals linked to the Ukraine war effort in recent years.

Tomasz Siemoniak, a Polish minister overseeing security services, said in a post on the social media platform X that last week’s arrest was carried out in cooperation with US authorities.