Pope Francis intends to travel to Türkiye next year to commemorate the anniversary of the First Council of Nicaea, the spiritual head of the world's Orthodox Christians said on Thursday.

The First Council of Nicaea, convened in 325, was a pivotal event in early Christianity where bishops convened to address theological controversies and establish foundational doctrines, resulting in the formulation of the Nicene Creed.

"His Holiness Pope Francis wishes to celebrate this important anniversary together," Ecumenical Patriarch Bartholomew, who is based in Istanbul, said at an event in the Portuguese capital, Lisbon.

He said Francis was planning to visit the Ecumenical Patriarchate of Constantinople in Istanbul before heading to the city of Iznik, where the First Council of Nicaea took place.

Ecumenical Patriarch Bartholomew said a committee was being formed to organize the visit and that the Vatican would soon contact the Turkish government about it.

Francis will turn 88 in December. International travel for him is increasingly difficult, given his health.

He uses a cane or a wheelchair to move around because of a knee problem, and earlier this year avoided public speaking and skipped important engagements on several occasions, including a Good Friday procession in March.

However, he is scheduled to travel to Indonesia, Papua New Guinea, Timor-Leste and Singapore in early September, and is expected to visit Belgium later that month.