A Russian court will take almost two weeks to hear a lawsuit filed by the mother of the Russian opposition leader Alexei Navalny contesting officials’ refusal to release her son’s body. 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. A closed-door hearing has been scheduled for 4 March, Russian state media said on Wednesday, citing court officials. Lyudmila Navalnaya on Tuesday appealed to Russian president, Vladimir Putin, on Tuesday to release her son’s body so he could be “buried humanely”. “For a fifth day I cannot see him, they aren’t giving me his body and don’t even tell me where he is,” she said, speaking in front of the prison colony where he son died, clad in black. “I appeal to you, Vladimir Putin. Resolving this issue depends on you alone. Let me finally see my son … I demand that Alexei’s body be released immediately so that I can bury him humanely.” More than five days after his death, his mother and a lawyer have been unable to retrieve Navalny’s body from investigators, who said they might not return it for two weeks as they run “tests”. Supporters believe he was murdered, either as an act of foul play or through mistreatment over three years in the Russian prison system. Navalny’s wife, Yulia Navalnaya, on Tuesday publicly accused Vladimir Putin of ordering the murder of her husband and said investigators were retaining his body in order to cover up a political assassination. Russia’s prison authorities reported on Friday that Navalny felt unwell after a walk and soon became unconscious at the prison in the town of Kharp. An ambulance arrived but he could not be revived, the service claimed, adding that the cause of death was still “being established”. Navalny’s death has triggered widespread condemnation in the west, with many leaders pledging to introduce new sanctions on the Kremlin. The UK on Wednesday imposed sanctions on six individuals in charge of the Arctic penal colony where Navalny died last week, in a largely symbolic measure that is unlikely to have any wider consequences for Russia. The Biden administration has also announced that it was preparing “major sanctions” against Moscow in response to Navalny’s death. Meanwhile, the imprisoned Russian-British opposition figure Vladimir Kara-Murza accused Putin of being behind Navalny’s death. “I know one thing for sure – Vladimir Putin is personally responsible for the death of Alexei Navalny,” Kara-Murza, who is serving a 25-year prison sentence for his outspoken criticism of the war in Ukraine, wrote from jail in a message passed on by his allies. On Monday, a UK Foreign Office minister ruled out a prisoner swap for Kara-Murza, who holds Russian and British citizenship and studied at the University of Cambridge. Since Navalny’s death, about 400 people have been detained across Russia as they tried to pay tribute to him with flowers and candles, according to one Russian group that monitors political arrests. Some of the Russian men detained while mourning have been handed military draft papers while in custody.