The wife of late Russian dissident Alexei Navalny said on Thursday that investigators had concluded his death in an Arctic prison colony in February was caused by a combination of diseases - a finding she rejected as preposterous.

Yulia Navalnaya said she would demand a criminal investigation of her husband's death, which she considers to be murder, and that Navalny's team would continue to conduct its own investigation.

Navalny, 47, died suddenly on Feb. 16. The Kremlin has rejected his supporters' accusation that President Vladimir Putin had him murdered. His death certificate said he died of natural causes.