MOSCOW (AP) — Tens of thousands of people are protesting across Russia to demand the release of jailed opposition leader Alexei Navalny in wave of nationwide demonstrations that have rattled the Kremlin.

Many chanted slogans against President Vladimir Putin. Activists say police detained more than 3,300 protesters across the country on Sunday, including over 900 in Moscow.

The authorities mounted a massive effort to stem the tide of demonstrations after tens of thousands rallied last weekend in the most widespread show of discontent Russia has seen in years.

Navalny, an anti-corruption activist, is Putin's most well-known critic. The United States urged Russia to release him and criticized the crackdown against protesters.