A spokesman at Russia's Orthodox Church in Moscow says church elders have chosen Metropolitan Kirill as their interim leader, following the death this week of Patriarch Alexei at the age of 79.
The 12 senior clergy known as the Holy Synod elders reached their decision late Saturday, after a meeting at the patriarchal residence in the village of Peredelkino.
A permanent partriarch is due to be selected within the next six months.
A church spokesman says Patriarch Alexei died Friday at his residence outside Moscow. He had long suffered from a heart condition.
Alexei's body will be taken to Moscow's Christ the Savior Church for three days of public viewing. Burial will take place at Epiphany (Russian: Bogoyavlensky) cathedral, also in Moscow.
Metropolitan Kirill formerly served as the church's foreign relations chief.
Alexei became leader of the church in 1990, as the officially atheist Soviet Union was loosening its restrictions on religion. After the Soviet Union collapsed the following year, the church's popularity surged.
In one of his biggest achievements, the patriarch signed a pact in May 2007 with Metropolitan Laurus, the leader of the Russian Orthodox Church Abroad, ending an 80-year split. The church abroad broke away after the Russian Revolution when clergy in Moscow fell under the influence of communist authorities.
Alexei was a strong defender of Russia's Orthodox traditions and strongly opposed any expansion of Roman Catholic or Protestant influence in Russia.
Despite longstanding tensions with the Vatican, Pope Benedict XVI praised Alexei on Friday for the "rebirth of the church" following the "severe ideological repression" of the Soviet era.
Alexei Mikhailovich Ridiger was born in 1929 in Tallinn, Estonia.
The son of a priest, Alexei accompanied his family on pilgrimages to churches and monasteries in what was then the Soviet Union. He said his family's many ventures to the key religious sites were crucial to setting his future path.
Researchers suggest Alexei's career may have been aided by assistance he gave the KGB (the Soviet security service) while a young priest in Tallinn. Orthodox Church officials vehemently deny the allegations.
Some information for this report provided by AP and AFP.