Senior Orthodox cleric Metropolitan Hilarion said that long-standing differences between the two churches remain, most notably a row over the status of the Uniate Church, in Ukraine.

But he said these differences were being put aside so that Patriarch Kirill and Pope Francis could come together over persecution of Christians.

This issue will be the central item on the agenda for their meeting, in Havana, Cuba, the cleric said.

"The situation shaping up today in the Middle East, in North and Central Africa, and in some other regions where extremists are carrying out a genuine genocide of the Christian population, demands urgent measures and an even closer cooperation between the Christian churches," Hilarion said.

"We need to put aside internal disagreements at this tragic time and join efforts to save Christians in the regions where they are subject to the most atrocious persecution."