The Kremlin on Monday confirmed an investigation into the death of imprisoned Russian opposition leader Alexei Navalny is ongoing and insisted that “all due actions are being taken” to determine the circumstances surrounding his demise.

Navalny, 47, was a well-known figure in Russia and a vocal critic of Russian President Vladimir Putin. He died in an Arctic penal colony, where had been serving a 19-year prison term.

World leaders reacted with dismay and suspicion to the news, while Navalny’s allies say the anti-corruption campaigner was likely murdered on Putin’s orders. The Kremlin has rejected these allegations, with the Russian foreign ministry calling the reaction from political leaders “self-exposing,” given that no forensic medical examination has yet been made available.

“The investigation is being carried out, all due actions are being taken. But no results of this investigation have been published so far, they are not known yet,” Kremlin spokesperson Dmitry Peskov said Monday at a daily news briefing, according to a NBC News translation.

“When there is no information, we consider it totally unacceptable to make such statements, which are quite rude and gross, to say frankly,” he added, referring to comments from political leaders blaming Putin for Navalny’s death.

U.S. President Joe Biden said Friday that “Putin is responsible” for Navalny’s death. “Make no mistake: Putin is responsible for Navalny’s death … What has happened to Navalny is yet more proof of Putin’s brutality.”

Asked whether the Kremlin was interested in a proper probe into Navanly’s death, Peskov replied, “Actions provided for by Russia’s legislation are being taken.”

Earlier on Monday, Navalny’s spokesperson Kira Yarmysh said that Navalny’s mother and lawyers had been blocked from entering a mortuary where his body could be being kept.

Yarmysh said on social media platform X that one of Navalny’s lawyers was “literally pushed out” and staff refused to answer questions about the whereabouts of his body.

CNBC could not independently verify the report. The Kremlin has denied any involvement in blocking the return of Navalny’s body to his relatives.

“This is not a question for us, we are not involved in this matter. This is not a function of the President’s Administration,” Peskov said.

Yulia Navalnaya, Navalny’s wife, on Monday said that she believed her husband was killed by Putin. In a video statement published on Navalny’s YouTube channel, Navalnaya vowed to continue his work and called on others to join her.

Navalny, who had been held behind bars in Russia since 2021, produced numerous reports on the corruption that had flourished during Putin’s leadership.

Famously, Putin has a long-running tradition of refusing to mention Navalny by name in public — a decision the Kremlin has previously said stems from the president’s views of the critic.

Navalny had sought to challenge Putin for Russia’s presidency, but his candidacy was barred in 2018. Putin will run for president once again next month, in an election where he faces only token opposition.