WARSAW, Poland (AP) — Polish authorities have arrested a man suspected of fatally shooting a Russian activist critical of President Vladimir Putin and Chechen leader Ramzan Kadyrov, and are investigating whether Russia is behind it, senior officials said Thursday.

The killing is the latest act which Polish authorities believe could be part of a campaign of Russian sabotage aimed at sowing fear and demoralizing Ukraine’s closest allies. Poland, a NATO and European Union member, has in recent years become a place of refuge for political dissidents from Russia and Belarus, as well as Ukrainian war refugees.