The head of the Greek Orthodox Church, Archbishop Christodoulos, is currently in the US undergoing liver transplant surgery, his church representatives have reported.
The operation is taking place at a hospital in Miami, Florida, and is expected to involve 10 hours in the operating room.
The development has come following news in June revealing that Archbishop Christodoulos, 68, was diagnosed with cancer after intestinal surgery.
The Greek Orthodox head travelled to Miami in August, but has been in waiting until only recently for a compatible liver donor.
Archbishop Christodoulos was elected head all Greece in 1998. Since being installed he has been a front-runner in efforts to bring a greater degree of unity between the Greek Orthodox and Roman Catholic Churches.
He met the Pope at the Vatican in 2006, in a meeting that was the first of its kind between Greece's most senior cleric and the leader of the world's Roman Catholics.
Following that historic meeting, reports explained that the two leaders had focused on attempts to reconcile ties following the 11th Century Great Schism.
