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Russian Orthodox Patriarch Alexy II, who presided over a vast post-Soviet revival of faith but was accused of making the church a force for nationalism, died Friday at age 79, the church headquarters said.

The Moscow Patriarchate said he died at his residence outside Moscow, but did not give a cause of death. Alexy had long suffered from a heart ailment.

Alexy 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. Church domes that had been stripped of their gold under the Soviets were regilded, churches that had been converted into warehouses or left to rot in neglect were painstakingly restored and hours-long Masses on major religious holidays were broadcast live on national television.

By the time of Alexy's death, the church's flock was estimated to include about two-thirds of Russia's 142 million people, making it the world's largest Orthodox church.

But Alexy often complained that Russia's new religious freedom put the church under severe pressure and he bitterly resented what he said were attempts by other Christian churches to poach adherents among people who he said should have belonged to the Orthodox church.

These complaints focused on the Roman Catholic Church, and Alexy refused to agree to a papal visit to Russia unless the proselytization issue was resolved.

"Patriarch Alexy II was tasked with leading the Church at a time of great transformation," the secretary of the Pontifical Council for the Promotion of Christian Unity, Monsignor Brian Farrell, told the ANSA news agency. "He was able to carry out this task with a great sense of responsibility and love of the Russian tradition."

Alexy lived long enough to see another major religious dispute resolved. In 2007, he signed a pact with Metropolitan Laurus, the leader of the breakaway Russian Orthodox Church Outside Russia, to bring the churches closer together. The U.S.-based ROCOR had split off in 1927, after the Moscow church's leader declared loyalty to the Communist government.

Alexy successfully lobbied for the 1997 passage of a religion law that places restrictions on the activities of religions other than Orthodoxy, Islam, Judaism and Buddhism. Under his leadership, the church also vehemently opposed schismatic Orthodox churches in neighboring Ukraine, claiming the Ukrainian church should remain under Moscow's control.

He was born Alexei Mikhailovich Ridiger on Feb. 23, 1929 in Tallinn, Estonia. The son of a priest, Alexy often accompanied his parents on pilgrimages to churches and monasteries, and he helped his father minister to prisoners in Nazi concentration camps in Estonia. It was during those visits that Alexy decided to pursue a religious life.

Under Soviet rule, this was not an easy choice. Lenin and Stalin suppressed religion and thousands of churches were destroyed or converted to other uses, such as museums devoted to atheism or, in some cases, stables. Many priests and parishioners were persecuted for their beliefs.

The persecution eased somewhat during World War II, when Stalin discovered that the church could be used as a propaganda tool in the fight against the Nazis. But the Soviet authorities never fully loosened their grip, penetrating the church at the highest levels.

Alexy was ordained in 1950, progressed through the Orthodox hierarchy, and was consecrated Bishop of Tallinn and Estonia in 1961.

The British-based Keston Institute, which monitors religious freedom in former Communist countries, has cited research suggesting that Alexy's career may have been aided by assistance he gave the KGB while a young priest in Tallinn. Orthodox Church officials vehemently denied the allegations.