MOSCOW, Russia (CNN)  -- Members of a Russian doomsday cult barricaded themselves in a cave to wait out the end of the world as the cult's leader underwent psychiatric exams Thursday, Russian media reported.



The cult, which calls itself the "true Russian Orthodox Church," believes the world will end in May.



The cult leader is in police custody awaiting proceedings on charges that he set up an organization "whose activity is associated with violence on citizens and instigation to refuse to perform their civil duties," according to the state-funded Itar-Tass news agency.



Four children are among 29 cult members holed up in a ravine in Russia's Penza region, where they apparently dug a cave.



One of the children in the cave is 18 months old, reported Itar-Tass. Temperatures in the cave are below 54 degrees Fahrenheit (12 degrees Celsius), the Russian news agency reported.



The cult members have refused law enforcement requests to come out or release the children, and they have threatened to commit suicide if police resort to force, according to Russian state television.



The cult, which calls itself the "true Russian Orthodox Church," believes the end of the world will come in May 2008.



Prosecutors announced Thursday they are opening criminal proceedings against the cult's leader, Father Pyotr Kuznetsov. Kuznetsov, 43, is "under the supervision of investigators," Olig Troshin, a Penza prosecutor, told Itar-Tass.



A law enforcement source in Penza told the Russian news agency Interfax that Kuznetsov "is being examined by psychiatrists."



Several clergymen, police officers and agents of the Russian Ministry for Emergency Situations are outside the cave.



"It is obviously some kind of insanity," Mitropolitan Kirill, a high-ranking Russian Orthodox Church official, told Russian television. "It is perhaps even a medical case. A very dangerous phenomena is happening in Russia's religious life."



He added, "What we're seeing in Penza right now is a most vivid example of what could happen to a country, to a society, if this society is deprived of proper religious education." E-mail to a friend



CNN's Maxim Tkachenko contributed to this report.
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