President Biden put the blame for Russian opposition leader Alexei Navalny's death squarely on the shoulders of Russian President Vladimir Putin, and said he hoped the tragedy spurs the U.S. Congress to give Ukraine more military aid to fight Moscow.

Speaking at the White House, Biden said he was "both not surprised and outraged" by the news of Navalny's death.

Biden called Navalny a powerful voice for the truth. He praised the opposition leader for his courage standing up to the Kremlin and for fighting against corruption in his country.

"We don't know exactly what happened but there is no doubt that the death of Navalny was the consequence of something that Putin and his thugs did," Biden said.

Biden said his administration was looking at a range of options to respond to Navalny's death, but he did not provide any details.

He said the tragedy underscores the stakes for Congress, where a new package of aid for Ukraine has run into roadblocks. He reprimanded House Republicans who have held up the aid and said he hoped Navalny's death encouraged them to take action.

"I hope to God it helps," he said.

He said the "clock is ticking," and saved particular condemnation for former President Donald Trump — his likely opponent in the presidential election — for recently saying that he would not defend NATO allies who failed to spend enough on defense.

"Let me be clear. This is an outrageous thing for a president to say," Biden said. "I can't fathom — can't fathom — from Truman on, they're rolling over in their graves hearing this. As long as I'm president, America stands by our sacred commitment to our NATO allies as they have stood by their commitments to us repeatedly."

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