President Joe Biden met privately in California on Thursday with the widow and daughter of Kremlin opposition leader Alexei Navalny, who died last week in a Russian prison, the White House said.

Biden met with Yulia and Dasha Navalnaya in San Francisco "to express his heartfelt condolences for their terrible loss," a statement said, adding that Biden reaffirmed an announcement on Friday of new sanctions against Russia.

In his meeting, "the president expressed his admiration for Alexei Navalny's extraordinary courage and his legacy of fighting against corruption and for a free and democratic Russia," the statement said.

Biden "emphasized that Alexei's legacy will carry on through people across Russia and around the world mourning his loss and fighting for freedom, democracy and human rights."

Russian authorities said on February 16 that Navalny, 47, had died suddenly in custody.

As one of the last opponents to President Vladimir Putin still active in Russia, Navalny galvanized mass protests and won popularity with a series of investigations into state corruption.

He was poisoned with a Soviet-era nerve agent in 2020 and was then jailed in 2021 after returning to Russia following a period of treatment in Germany.

He was sentenced to 19 years in prison on extremism charges and sent to IK-3, a harsh penal colony beyond the Arctic Circle known as "Polar Wolf."

Navalny's mother, Lyudmila Navalnaya, said Thursday that authorities were trying to force her to carry out his burial in secret.

US National Security Council spokesman John Kirby told journalists that Russian authorities should return the campaigner's body to his mother so that she can "properly memorialize... her son's bravery and courage and service."

Earlier, the US government marked the upcoming two-year anniversary of Russia's invasion of pro-Western Ukraine by unsealing charges against a series of wealthy Russians to help cut the "flow of illegal funds that are fueling" Moscow's war.

Sanctions specifically aimed at responding to the death of Navalny were due to be announced Friday.