The Biden administration is preparing “major sanctions” against Moscow in response to the death of the Russian opposition leader Aleksei A. Navalny, a White House official said on Tuesday.

John F. Kirby, a National Security Council spokesman, said the sanctions would be announced on Friday. President Biden has said there is “no doubt” that Vladimir V. Putin’s government was behind the death of Mr. Navalny.

“Whatever story the Russian government decides to tell the world, it’s clear that President Putin and his government are responsible for Mr. Navalny’s death,” Mr. Kirby told reporters on Tuesday.

Mr. Kirby declined to detail what would be included in the sanctions package but said it would be devised to “hold Russia accountable for what happened to Mr. Navalny and, quite frankly, for all its actions over the course of this vicious and brutal war that has now raged on for two years.”

Russian officials have said Mr. Navalny, 47, lost consciousness and died after taking a walk on Friday in the Arctic prison where he was moved last year. Russia has announced an investigation into Mr. Navalny’s death, but Mr. Kirby said on Tuesday that “regardless of the actual scientific answer, Mr. Putin is responsible for it.”

“Absent some credible investigation into his death, it’s hard to get to a point where we can just take the Russians’ word for it,” he said.

Mr. Navalny’s death came as Russia’s invasion of Ukraine neared the end of its second year and billions of dollars in U.S. aid remained stuck in Congress. Mr. Navalny, who was one of Mr. Putin’s fiercest critics, was also a forceful voice in condemning the invasion.

“One of the most powerful things that we can do right now to stand up to Vladimir Putin, of course, is to again pass the bipartisan national security supplemental bill and support Ukraine as they continue to fight bravely in defense of their country,” Mr. Kirby said.

Since Russia’s invasion in 2022, the Biden administration has announced a series of sanctions that the United States hoped would hobble Russia economically and militarily. Washington has cut off Russia’s largest banks and companies from Western financial markets, joined with Europe to freeze hundreds of billions of dollars of Russian central bank assets, and joined its Group of 7 allies in taking steps to curb the flow of military technology to Russia.

But the sanctions have largely failed to alter the country’s ability to endure economically throughout the war as Mr. Biden had hoped. Just last month, the International Monetary Fund said Russia’s economy is actually growing faster than expected.

In response to a question about the effectiveness of previous sanctions, Karine Jean-Pierre, the White House press secretary, maintained that the United States and its partners had “imposed the most severe sanctions on Russia that any economy of its size has ever faced.”

“We’ve kicked them out of the international organization and worked to isolate them on the world stage,” she added.