The head of the Russian Orthodox Church, Patriarch Alexy II, and the leader of the church's branch in exile, Metropolitan Lavr, signed the historic reunification agreement during an elaborate ceremony at Moscow's largest cathedral.

"By this Act, canonical communion within the Local Russian Orthodox Church is hereby restored," the act read, according to a transcript published on the web site of the Russian Orthodox Church Outside Russia.

Dozens of bearded priests flanked Alexy II, dressed in flowing green robes, while he and the blue-clad Lavr signed the act and embraced.

Putin then stepped forward to accept Alexy's congratulations for his "service to the faith and country."

The Russian leader, a former KGB officer who has since publicly embraced Christianity, told the thousands gathered that the reunification was a moment of renaissance for the country.

"The rebirth of church unity today is the most important condition for restoring the lost unity of the entire Russian world," Putin said in remarks broadcast on state-run television.

At the culmination of the service, the once rival church leaders were due to take communion from the same chalice in a gesture to seal the spiritual reunification.