A Russian court has rejected legal action brought by the mother of Alexei Navalny, his foundation says.
Lyudmila Navalnaya had filed a claim of improper provision of medical care against the Arctic penal colony where her son was imprisoned when he died.
Announcing his death last month, prison officials said he had gone for a walk, said he felt unwell, then collapsed and never regained consciousness.
His widow said he was killed on the orders of President Vladimir Putin.
For years, Navalny was Russia's most high-profile critic of Mr Putin. In 2022, he was sentenced to 19 years on charges that were widely seen as politically motivated.
His team said Navalny had filed his own lawsuits for failure to provide medical care many times during the three years he spent in prison, but all were denied.
Nicknamed Polar Wolf, the penal colony is known for a culture of collective punishment.
The director of Navalny's foundation claimed the letter received by Ms Navalnaya suggested that only Navalny himself could be a plaintiff in the claim.
"I wonder how?" Ivan Zhdanov said in a post on Telegram.
Yulia Navalnaya also reacted to the news on social media, claiming on X, formerly known as Twitter, that the case was dismissed to avoid evidence of her late husband's death being aired in court.
"There is only one reason [the case was dismissed] - at the trial, they have to provide documents and videos about what happened on 16 February," she said.
The Kremlin denied allegations that Navalny was murdered by Russian authorities, calling Western reaction to his death "hysterical".
For more than a decade, Mr Putin refused to refer to his political opponent by name, but this changed after his death.
"As for Navalny, yes he passed away, this is always a sad event," Mr Putin said after claiming his fifth term as president.
