Russian law enforcement authorities decided to extend a preliminary investigation into the death of Alexei Navalny at an Arctic prison earlier this year, the late opposition activist’s allies said Tuesday.Navalny was serving a 19-year prison sentence on extremism charges when he died under unclear circumstances at the “Polar Wolf” penal colony on Feb.

16.

Authorities in the Yamal-Nenets autonomous district, where the prison was located, initially refused to open a criminal investigation, stating that his death was due to “combined diseases” rather than criminal activity.However, regional prosecutors overturned that decision on Aug.

16, instructing investigators to continue their probe, according to a letter addressed to Navalny’s lawyer, Vasily Dubkov, dated Aug.

30.“This doesn’t mean that a criminal case will be opened, only that the investigation will continue,” said Ivan Zhdanov, a longtime Navalny ally living in exile.

He suggested the Russian authorities may be trying to reframe the circumstances of the activist’s death or prolong the probe indefinitely.More than 180 Russian doctors signed an open letter last month urging federal investigators to charge prison staff with negligence in connection with Navalny’s death, and accusing President Vladimir Putin of ignoring warnings about the life-threatening conditions of Navalny's detention.