Poland has foiled a Russian plot to kill a Ukrainian American citizen in Warsaw, Polish Prime Minister Donald Tusk said Thursday. He described it as the first time that “someone on the order of Russia” had sought to attack a US citizen on the territory of another NATO country.

The suspect, who was allegedly recruited by Russia’s secret services, was detained by Polish authorities on August 7. Warsaw police said he will be held in custody for three months.

Tusk said the American Ukrainian citizen was “uncomfortable for the Putin regime,” but did not provide further details about the alleged target.

The operation was carried out in cooperation with US services, according to Tomasz Siemoniak, Poland’s minister overseeing intelligence services. He said the targeted victim was a US citizen “of Ukrainian origin.” Officials did not immediately provide additional information.

Western officials have previously warned that Russia has stepped up a campaign of targeted killings since President Vladimir Putin’s 2022 invasion of Ukraine. Several alleged plots have been disrupted across Europe, including attempts targeting Russian activists, supporters of Ukraine and military defectors.

Tusk said Poland and other countries must be prepared for attempts by the Putin regime to eliminate people who are considered inconvenient.

Western officials view the alleged campaign as part of broader Russian efforts to undermine European countries supporting Ukraine. The AP has mapped about 200 acts of sabotage, arson and other disruption across Europe since the start of the war that officials have linked to Russia.

Previous cases cited by officials include the 2006 killing of former FSB officer Alexander Litvinenko in London, the attempted poisoning of former Russian military intelligence officer Sergei Skripal in 2018, and the 2019 killing of former Chechen rebel commander Zelimkhan Khangoshvili in Berlin.

Polish authorities also arrested a man in 2024 over what they said was a plot to assassinate Ukrainian President Volodymyr Zelenskyy.