Arrests of Europeans for Aiding Russia Raise Fears of Kremlin’s Reach

The authorities in Poland and Germany have arrested at least five of their citizens in recent days and accused them of spying for Russia or of offering to help Moscow commit violence on European soil, including a “possible attack” on the president of Ukraine, Volodymyr Zelensky.

The arrests underscored fears of the Kremlin’s furtive network in the West and its use of foreign nationals, including violent criminals and soccer hooligans, to terrify or possibly even kill opponents sheltering abroad.

The Polish National Prosecutor’s Office said in a statement that a Polish citizen, identified as Pawel K., was detained on Wednesday. It said he had offered to assist Russian agents in a possible plot aimed at killing Mr. Zelensky.

It gave few details, other than saying he had “declared his readiness to act for the military intelligence of the Russian Federation and established contacts with citizens of the Russian Federation directly involved in the war in Ukraine.”

Prime Minister Donald Tusk of Poland said on Friday that the police had also arrested two Polish citizens for attacking a top aide to the Russian opposition campaigner Aleksei A. Navalny outside the aide’s home in Vilnius, the capital of Lithuania, last month with a hammer. The Polish leader said a citizen of Belarus, who allegedly had ordered up the attack on Moscow’s behalf, had also been apprehended. Mr. Navalny died in Russian prison in February.

“There will be no leniency for collaborators with the Russian services,” Mr. Tusk said in his statement on Friday. He vowed to stamp out “every betrayal and attempt at destabilization.”