During a visit to a Rome basilica, where he met migrants, Francis told of his visit to a camp on the Greek island of Lesbos last year.
There he met a Muslim refugee from the Middle East who told him how "terrorists came to our country". Islamists had slit the throat of the man's Christian wife because she refused to throw her crucifix the ground.
"I don't know if he managed to leave that concentration camp, because refugee camps, many of them, are of concentration (type) because of the great number of people left there inside them," the pope said.
Francis praised countries helping refugees and thanked them for "bearing this extra burden, because it seems that international accords are more important than human rights".
He did not elaborate but appeared to be referring to agreements that keep migrants from crossing borders.
In February, the European Union pledged to finance migrant camps in Libya as part of a wider European Union drive to stem immigration from Africa.
Humanitarian groups have criticized efforts to stop migrants in Libya, where - according to a U.N. report last December - they suffer arbitrary detention, forced labor, rape and torture.
Last year the EU and Turkey reached a deal to send back irregular migrants from the Greek Aegean islands to Turkey in exchange for political and financial rewards for Ankara. The agreement was criticized by rights groups.
The pope urged people in northern Italy, home to an anti-immigrant party, to take more migrants, hoping that the generosity of southern Italy could "infect the north a bit".
Noting that Italy had one of the world's lowest birth rates, he said: "If we also close the door to migrants, this is called suicide."
The basilica of St Bartholomew is a shine to Christians killed for their faith in the 20th and 21st century.
It contains a prayer book used by Father Jacques Hamel, the 85-year-old French priest killed by Islamist militants who stormed into a church in Saint-Étienne-du-Rouvray last year, forced Hamel to his knees, and slit his throat while they chanted in Arabic. His sister Roselyne attended the service.
Banner and thumbnail credit: Reuters