Pope Francis will enter one of the controversial migrant sorting centres backed by the European Union during his Saturday visit to the Greek island of Lesbos, the Vatican said two days ahead of the trip.
So-called hotspots register incoming migrants and distinguish those with legitimate asylum claims from the rest who need be repatriated. The ones in Greece are instrumental in a new EU-Turkey migrant-swapping deal strongly criticized by humanitarian groups.
Francis will visit Lesbos' Moria hotspot, hosting about 2,500 people, with Orthodox church leader, Patriarch Bartholomew of Constantinople, and the Orthodox Archbishop of Athens and All Greece, Ieronymos, the Vatican said in a news briefing.
The three men will travel to the site in a minibus, personally greet about 250 refugees, make speeches, sign a joint declaration on the migration crisis, and sit down for lunch with a small group of Moria residents.
Later, Francis, Bartholomew and Ieronymos will meet the local population and Lesbos' small Catholic minority at the island's port, where each religious leader will say prayers and throw a laurel wreath in the sea to commemorate dead migrants.
Greek Prime Minister Alexis Tsipras is expected to be present throughout the visit, welcoming Francis at the airport and sending him off, but will not make any public adress, Vatican spokesman Father Federico Lombardi said.
Lombardi described the papal trip was "a strictly humanitarian and ecumenical" affair, and ducked questions on whether it represented an implicit criticism of the EU's recent migrant repatriation deal with Turkey.
The spokesman said it was "possible" that the pope may offer financial aid during the visit.
Francis is an outspoken champion of migrant rights.
His first visit outside the Vatican, in 2013, was to the Italian island of Lampedusa, another landing point for migrants and refugees bound for Europe. A year later he told the European Parliament: "We cannot allow the Mediterranean to become a vast graveyard."
Last month, he celebrated the pre-Easter ritual of the washing of the feet in a refugee shelter outside Rome, performing it on three Muslim men, a Hindu from India, three Orthodox Coptic women from Eritrea, four Catholic men from Nigeria and an Italian female charity worker.