U.S. President Joe Biden reacted to the death of Russian opposition leader Alexey Navalny Friday, directly blaming Russian President Vladimir Putin and using the death to scold the U.S. House of Representatives for holding up funding for Ukraine.

Russian prison officials say Navalny, a fierce foe of the Russian president, died in the Russian Arctic labor camp where he was imprisoned. The official statement has not been independently confirmed.

Russian media quoted officials of the Federal Prison Service saying medical staff had been called but were unable to resuscitate the 47-year-old Navalny.

In a statement in the Oval Office at the White House, Biden praised Navalny for his courage in continually standing up to Putin, even after he was poisoned, treated overseas and then imprisoned when he returned to Russia.

President Joe Biden delivers remarks on the death of Russian opposition leader Alexei Navalny, in the Roosevelt Room of the White House, Feb. 16, 2024, in Washington.

President Joe Biden delivers remarks on the death of Russian opposition leader Alexei Navalny, in the Roosevelt Room of the White House, Feb. 16, 2024, in Washington.

“He could have lived safely in exile …,” following an assassination attempt in 2020, Biden said. “Instead, he returned to Russia knowing he’d likely be imprisoned, or even killed if he continued his work. But he did it anyway. Because he believed so deeply in his country.”

Biden said Russian officials will tell their own story, but said, “Make no mistake: Putin is responsible for Navalny’s death.”

He said Navalny’s death is a reminder of the stakes of this moment and once again appealed to the U.S. House of Representatives to vote on the bipartisan aid package approved this week by the U.S Senate. Biden said “history is watching” the House of Representatives.

“The failure to support Ukraine at this critical moment will never be forgotten,” Biden said.

Officials say an investigation has been launched to determine the cause of Navalny’s death.

He was serving a 19-year sentence on charges of extremism. He was moved from his former prison in the Vladimir region of central Russia to a maximum-security penal colony in the town of Kharp, in the Yamalo-Nenets region, about 1,900 kilometers northeast of Moscow, above the Arctic Circle.

FILE - Russian opposition leader Alexei Navalny appears on a video link from prison provided by the Russian Federal Penitentiary Service at Moscow City Court, May 24, 2022.

FILE – Russian opposition leader Alexei Navalny appears on a video link from prison provided by the Russian Federal Penitentiary Service at Moscow City Court, May 24, 2022.

In a post on the social media platform X shortly after the announcement, Navalny’s chief of staff Leonid Volkov and his spokesperson Kira Yarmysh wrote they had no confirmation of his death. The post said Navalny’s lawyer was on his way to Kharp and promised a report as soon as they receive information.

Navalny had been behind bars since January 2021, when he returned to Moscow after recuperating in Germany from nerve agent poisoning that he blamed on the Kremlin. Since then, he received three prison sentences, all of which he rejected as politically motivated.

Praise for Navalny’s bravery poured in from Western leaders and others who have opposed Putin’s leadership. The opposition leader’s health has deteriorated recently, and the cause of death remains unknown, but many world leaders said they held Russian authorities ultimately responsible for his death.

Speaking on the sidelines of the Munich Security Conference, NATO Secretary-General Jens Stoltenberg said Navalny has been a strong voice for freedom and democracy for many years. He said NATO and NATO allies have long called for his release.

Stoltenberg said all the facts must be established and Russia has serious questions to answer.

During a joint news conference in Berlin alongside German Chancellor Olaf Scholz, Ukraine’s president, Volodymyr Zelenskyy, was typically blunt when reacting to the reports of Navalny’s death.

“Obviously he was killed by Putin,” Zelenskyy said. “Like thousands of others who have been tortured, tortured because of this one creature. Putin doesn’t care who dies.”

Zelenskyy said Putin must lose everything and be held accountable for his actions.

Some information for this report was provided by The Associated Press, Reuters and Agence France-Presse.