Pope Francis urged governments on Saturday to get migrants and refugees out of holding centres, saying many had become "concentration camps".

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.