International concern is growing for Vladimir Putin's main opponent Alexei Navalny, after his allies said he has been removed from the Russian penal colony where he had been imprisoned since mid-2022.
The opposition politician's location inside the prison system remains unknown and he again did not show up at a court hearing by video link, Kira Yarmysh, his spokesperson, said on Tuesday.
The United States is deeply concerned for Mr Navalny's wellbeing, State Department spokesperson Matthew Miller said on Monday.
The US has communicated to the Russian government that they are responsible for what happens to the Russian opposition politician, Mr Miller told reporters.
Before his 'disappearance' from the prison system, Mr Navalny's allies had been preparing for his expected transfer to a "special regime" colony, the harshest grade in Russia's prison system.
The transfer was expected after Mr Navalny was sentenced in August to an additional 19 years in prison, on top of the eleven-and-a-half years he was already serving.
The process of moving prisoners by rail across Russia's vast territory can take weeks, with lawyers and family unable to obtain information about their location and well-being until they reach their destination.
It was unclear if Mr Navalny was already in transit to a new prison.
His spokesperson, Kira Yarmysh, said on Monday that staff at the IK-6 facility in Melekhovo, 235 km (145 miles) east of Moscow, had said Mr Navalny was no longer among its inmates.
On Tuesday, Ms Yarmysh wrote on X, formerly known as Twitter: "Today Alexei was again not brought to court to appear by video link, but now nobody is talking nonsense about an 'electricity accident'.
"An employee of penal colony-6 stated that Alexei had 'left their colony, but that he allegedly did not know where he had been transferred to'."she wrote.
Ms Yarmysh suggested that an initial explanation that was given for six days, that claimed an electricity problem had been responsible for Mr Navalny's non-appearance in court had been a ruse by the authorities to play for time.
There was no immediate comment from Russia's prison service.
Mr Navalny's disappearance came at the start of the campaign period for a presidential election in March at which Vladimir Putin is expected to win another six-year term.
