A prominent Russian opposition activist and Washington Post contributor who denounced the invasion of Ukraine was sentenced to 15 days in jail in Moscow Tuesday for "disobeying a police order," per NPR.

Why it matters: U.S. officials and the Washington Post are calling for the release of Vladimir Kara-Murza, who was detained near his Moscow home on Monday — hours after CNN published an interview with the reportedly twice-poisoned Putin critic in which he called the Kremlin "a regime of murderers."

What they're saying: Secretary of State Antony Blinken tweeted Monday that the U.S. was "troubled by Russian authorities' detention today in Moscow of prominent civil society leader Vladimir Kara-Murza."

• "We are monitoring this situation closely and urge his immediate release," Blinken added.

The Washington Post published an editorial condemning the 40-year-old Russian journalist's arrest on Tuesday, headlined, "Vladimir Kara-Murza's arrest is spurious. The dictatorship is real."

• WashPost publisher Fred Ryan said in a statement that after "poisonings and other grave threats, this outrageous detention is the latest move in Vladimir Putin’s ongoing effort to silence Kara-Murza and hide the truth about the atrocities Putin is committing in the Russian people's name."
• "No one should be deceived by the Russian government’s trumped-up charges and smears, and Kara-Murza should be released immediately," he added.

The big picture: Kara-Murza ended up in a coma in 2015 and again in 2017 after, he said, he was poisoned in attacks by the Kremlin launched because he called for Western sanctions against Russia's government, per WashPost.

• "Investigations by independent organizations found that he had been followed by members of the same federal agency that allegedly poisoned jailed Kremlin critic Alexei Navalny and at least three other opposition figures," WashPost notes.
• The Kremlin denies any wrongdoing in Kara-Murza's hospitalizations.