Pope Francis will receive Russian President Vladimir Putin on Nov. 25, an encounter that could help mend strained relations between the Vatican and the Russian Orthodox Church.
Russian-Vatican relations have been fraught since the 1991 breakup of the Soviet Union, with Moscow accusing the Roman Catholic Church of trying to poach believers from the Russian Orthodox Church, a charge the Vatican denies.
But Putin is the first Kremlin leader since the 1917 Bolshevik Revolution to publicly profess religious faith — to the Orthodox church — and has several times advocated ending the long feud between the two major Christian churches.
Putin, who also met the pontiff's two immediate predecessors, could invite the pope to visit Russia, diplomats said.
Popes Benedict and John Paul had standing invitations from the Russian government but could not go because they received no matching invitation from the Orthodox Church. Francis would need the same to go to Russia.
Another dispute between the churches concerns the fate of many church properties that Soviet leader Joseph Stalin ordered confiscated from Eastern Rite Catholics, who worship in an Orthodox liturgy but owe their allegiance to Rome.
Stalin gave the Catholic property to the Russian Orthodox Church, but after the fall of communism, the Eastern Rite Catholics took back many sites, leading to a rise in tensions.
The Russian Orthodox Church, which has resurged since the collapse of the Soviet Union, has some 165 million members in former Soviet republics including Russia and other states.
Francis is the first non-European pope in 1,300 years. His predecessors came from countries — Italy, Poland and Germany — that were caught up in the 20th century's two global conflicts as well as in the Cold War that followed World War Two.
Diplomats have said that Francis, an Argentine with no European political baggage, would have a far better chance of improving ties with the Russian Orthodox Church.
There have been signs of a general warming between the western and eastern branches of Christianity.
On March 20, Ecumenical Patriarch Bartholomew became the first worldwide spiritual leader of Orthodox Christians to attend a papal inaugural Mass since the Great Schism split western and eastern Christianity in 1054.