The mother of Russian opposition leader Alexei Navalny has filed a lawsuit at a court in the Arctic city of Salekhard contesting officials` refusal to release her son`s body, Russia`s state news agency Tass reported Wednesday.

A closed-door hearing has been scheduled for March 4, the report said, quoting court officials.

Lyudmila Navalnaya has been trying to retrieve her son`s body since Saturday, following his death in a penal colony in Russia`s far north a day earlier. She has been unable to find out where his body is being held, Navalny`s team reported, reports AP.

Navalnaya appealed to Russian President Vladimir Putin Tuesday to release her son`s remains so that she could bury him with dignity.

"For the fifth day, I have been unable to see him. They wouldn`t release his body to me. And they`re not even telling me where he is," a black-clad Navalnaya, 69, said in the video, with the barbed wire of Penal Colony No. 3 in Kharp, about 1,900 kilometers (1,200 miles) northeast of Moscow.

"I`m reaching out to you, Vladimir Putin. The resolution of this matter depends solely on you. Let me finally see my son. I demand that Alexei`s body is released immediately, so that I can bury him like a human being," she said in the video, which was posted to social media by Navalny`s team.

Russian authorities have said the cause of Navalny`s death is still unknown and refused to release his body for the next two weeks as the preliminary inquest continues, members of Navalny`s team said.

They accused the government of stalling to try to hide evidence. On Monday, Navalny`s widow, Yulia, released a video accusing Putin of killing her husband and alleged the refusal to release his body was part of a cover-up.

"They are cowardly and meanly hiding his body, refusing to give it to his mother and lying miserably," she said.

Kremlin spokesman Dmitry Peskov rejected the allegations of a cover-up, telling reporters that "these are absolutely unfounded, insolent accusations about the head of the Russian state."

Navalny`s death has deprived the Russian opposition of its best-known and inspiring politician less than a month before an election that is all but certain to give Putin another six years in power.

Many Russians had seen Navalny as a rare hope for political change amid Putin`s unrelenting crackdown on the opposition.

Since Navalny`s death, about 400 people have been detained across in Russia as they tried to pay tribute to him with flowers and candles, according to OVD-Info, a group that monitors political arrests. Authorities cordoned off some of the memorials to victims of Soviet repression across the country that were being used as sites to leave makeshift tributes to Navalny. Police removed the flowers at night, but more keep appearing.

Peskov said police were acting "in accordance with the law" by detaining people paying tribute to Navalny.

Over 60,000 people have submitted requests to the government asking for Navalny`s remains to be handed over to his relatives, OVD-Info said.