MOSCOW — The family of Alexei Navalny, the Putin critic who died in a Russian prison, have reportedly been told his body will not be released for two weeks.

His mother was informed it was being held for "chemical analysis", a representative for Navalny said.

There has been no confirmation of the whereabouts of the body from Russian authorities, while efforts to locate it have been repeatedly shut down.

The wife of the late Russian opposition leader has accused them of hiding it.

In a video on Monday vowing to continue his work to fight for a "free Russia", Yulia Navalnaya directly accused Russian President Vladimir Putin of killing her husband. She also alleged his body was being kept until traces of poisoning by the nerve agent Novichok had disappeared.

Her voice sometimes shaking with grief and anger, Ms Navalnaya asked viewers to stand alongside her and "share the fury and hate for those who dared to kill our future".

Navalny's death in prison was announced on Friday. The authorities at the Siberian penal colony where he was being held said he had never regained consciousness after he collapsed following a walk.

His mother and lawyer traveled to the remote colony as soon as news of his death broke.

Attempts to locate the body have repeatedly been shut down by the prison mortuary and local authorities.

On Monday, the Kremlin said an investigation into Navalny's death was ongoing and that there were "no results" as of yet.

Later, Navalny's spokeswoman Kira Yarmysh said that investigators had told Navalny's mother Lyudmila they would not hand over the body for two weeks while they conducted a "chemical analysis".

In her video message, Ms Navalnaya said she believed the authorities were waiting for Novichok to disappear from Navalny's body.

Navalny, who was the Russian opposition's most significant leader for the last decade, had been serving a 19-year sentence on charges many viewed as politically motivated.

Western leaders have put the blame for Navalny's death squarely on President Putin.

Responding to questions from reporters on Monday, President Joe Biden said: "The fact of the matter is: Putin is responsible, whether he ordered it or he is responsible for the circumstances he put that man in."

During a press conference on Monday, EU foreign policy chief Josep Borrell said he Navalny had been "slowly murdered in a Russian jail by Putin's regime".

Both the EU and the US have said they are considering new sanctions on Russia following Navalny's death.

The UK Foreign Secretary, Lord Cameron, has also said he expects Britain and the rest of the G7 group of rich nations to impose fresh sanctions on any Russians involved in the death.

Kremlin spokesman Dmitry Peskov said comments by Western politicians in regards to Navalny's death were "arrogant" and "unacceptable".

Russian prison authorities said at the weekend that Navalny had suffered "sudden death syndrome". — BBC