WARSAW (AP) — A Russian plot to kill a Ukrainian American citizen in Warsaw was thwarted by Poland before it could be carried out, the Polish prime minister said Thursday.

It was the first time that “someone on the order of Russia” sought to attack an American citizen on the territory of another NATO country, Prime Minister Donald Tusk said.

A suspect, who was allegedly recruited by Russia’s secret services, was detained by Polish authorities on Aug. 7.

The American Ukrainian citizen “was uncomfortable for the Putin regime,” Tusk said in a news conference.

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

The Russian Foreign Ministry did not immediately respond to a request for comment.