Russian opposition leader Alexey Navalny has threatened to sue the prison in which he is jailed, accusing it of withholding the Quran – a holy book he intended to study while serving his sentence, writes AlJazeera.

In an Instagram post announcing his first lawsuit against prison officials, he said: “The thing is, they’re not giving my Quran”.

He added that “deeply studying” the Quran, which is the central religious text of Islam, was one of several “self-improvement” goals he had set for himself while in prison.

The claim comes as Navalny, a Christian, remains on a hunger strike in protest against an alleged refusal by authorities to allow his physician to examine him behind bars, after he developed severe back and leg pain.

The 44-year-old’s Instagram post came as the month of Ramadan began, a period in which Muslims fast from sunrise to sunset and spend time reading the Quran. Navalny’s claim may come as a surprise to some.

He came under fire early in his political career for making nationalistic comments and deriding immigrants in Russia from predominantly Muslim countries in Central Asia.

Navalny said he has not been given access to any of the books he brought or ordered over the past month because they all need to be “inspected for extremism”, which officials say takes three months.

“Books are our everything, and if I have to sue for my right to read, then I’ll be suing”, - he said.