(RNS) — Imprisoned Russian opposition leader Alexei Navalny is threatening to sue Russian authorities over access to Islam’s holy book.

“I realized that my development as a Christian also requires studying the Quran,” Navalny said in an Instagram post by his team on Tuesday.

Navalny, who has been called “the man Vladimir Putin fears most,” was ordered by a Russian court to serve a two and a half year prison term for violating the terms of his probation in February after a 2014 sentence for embezzlement. Part of those probation violations included a trip to Germany, which Navalny claimed he took to recover from being poisoned, an attempt on his life that he blames on Putin.

The European Court of Human Rights has found his most recent sentencing to be “arbitrary.”

Experts say the activist’s arrest, which sparked protests across Russia, was tied to his anti-corruption work. Following his imprisonment, the Navalny’s Anti-Corruption Foundation released a new documentary, “Putin’s Palace,” accusing Russian President Vladimir Putin of embezzling public funds.  

Navlany is serving his sentence at a penal labor colony near Moscow. In response to his treatment, he has also launched a hunger strike. His lawyers and representatives said he is suffering from weight loss and fatigue while in prison.

“They won’t give me my Quran. And it’s infuriating,” read the statement from the anti-corruption activist, lawyer and leader of the Russia of the Future Party.

“When I was jailed, I made a list of ways I wanted to improve myself that I will try to complete in jail. One of the points was to deeply study and understand the Quran,” he said. Navalny added that his goal was to become “the Quran champion” among Russia’s non-Muslim politicians.

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Navalny, who said he has previously read the Quran, has made a number of comments critical of Russian Muslims and Muslim immigrants to Russia. His post, timed to coincide with the start of Ramadan, may be designed to appeal to this important demographic in Russia.

In a 2015 blog post, he voiced support of Switzerland’s ban on the construction of minarets. In that same post he criticized the building of the Moscow Cathedral Mosque, whose grand opening in 2015 was attended by Putin.

“It is clear that this Islamophobe is trying to use the Holy Scriptures for his own political purposes and will definitely use quotes for provocations, as they have long learned to do in Europe,” wrote Ramzan Kadyrov, the head of the Chechen Republic in a post on his Telegram channel. He added, “On behalf of the Muslims of Russia, I appeal to the employees of the colony where the provocateur is being held: do not let the prisoner serving a fair sentence sow sectarian strife!”

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In the past Navalny has written critically of Islamic education in Chechnya, which is ruled by Kadyrov, a Putin loyalist. Navalny has questioned the role of Islam in governance in the Caucasus region and once referred to economic migrants from the North Caucasus, a Muslim-majority region, as “cockroaches.”

Muslims make up roughly 15% of Russia’s population and have been a recognized minority in the country since the time of Catherine the Great. Muslims make up the majority in seven regions of Russia, and the world’s largest country is an observer member of the Organization of Islamic Cooperation.