Mr. Kolker’s arrest was part of a flurry of detentions in recent weeks that have targeted a swath of society, including scientists, a top economist and a professional hockey player.

Dozens have been arrested for speaking out against the Kremlin’s invasion of Ukraine, including some of those arrested in recent weeks.

But in the case of others, the Kremlin appears to have targeted figures solely for appearing insufficiently patriotic at a time when the government of President Vladimir Putin is demanding unflinching support, say rights lawyers and political analysts. The harshness of some of the arrests is meant to put people on notice, they say…

Russian analysts and the country’s dwindling number of human-rights advocates say Moscow’s security services are taking a cue from Mr. Putin to root out anyone deemed disloyal to the Kremlin, and that the arrests suggest Russia is slipping into the kind of paranoia that gripped it during the Cold War, as the government seeks to squelch the smallest hint of resistance to Kremlin policies.