Police in Russia detained more than 400 people across the country at rallies honoring late opposition leader Alexei Navalny over the weekend, according to a list of detainees published by Russian human rights group OVD-Info on Saturday and reporting from Radio Free Europe on Sunday. Federal authorities announced earlier this week that Navalny died in an Arctic prison colony, where he was serving out a 30-year prison sentence.

OVD-Info reported that at least 133 detainees were held in St Petersburg and at least 50 in Moscow. Authorities in other cities were also making arrests. 19 people were detained in the city of Stavropol and 11 were detained in Ryazan. Supporters of Navalny had gathered to honor him and lay flowers in his memory.

Navalny, who rose to become Vladimir Putin’s most prominent opponent and anti-corruption leader, was announced dead on February 16 from unknown causes. Russia’s federal prison service said he “felt unwell after taking a walk, and began to lose consciousness almost immediately.” Navalny’s spokesperson has since said he was “murdered.” The suspicions around the cause of his death are strengthened by previous events that occurred in August 2020, when Navalny was left in a coma after being poisoned with a suspected nerve agent. He was later arrested on charges of having violated a probation order after his return from Germany, where he was recovering.

Following reports of Navalny’s death, US President Joe Biden delivered his reaction in a press conference, saying he was “both not surprised and outraged.” Biden accused Putin of being the principal culprit behind Navalny’s death, saying, “What happened to Navalny is yet more proof of Putin’s brutality.”

Navalny is not Putin’s first political opponent who died in suspicious circumstances. In 2015, Boris Nemtsov, a prominent Putin critic, was killed on a bridge just outside of the Kremlin. In August 2023, the leader of the powerful Russian mercenary group Wagner, Yevgeny Prigozhin, died in a plane crash following an attempted uprising against Moscow.

Other world leaders also expressed shock and outrage. German Chancellor Olaf Scholz said he was “deeply saddened” by Navalny’s death. French President Emmanuel Macron honored Navalny’s memory, stating that his death means the weakening of the Kremlin. UN Secretary-General Antonio Guterres expressed his shock at the news and called for a “full, credible, and transparent investigation into the circumstances of Mr. Navalny’s reported death in custody.”