The detention centers where Europe-bound refugees are held are like Nazi concentration camps, Pope Francis said Saturday.
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"Refugee camps are concentration camps" because they are so overcrowded, the pontiff said.
He spoke during a special religious service on Tiber Island in central Rome, commemorating modern-day Christian martyrs.
In an off-the-cuff addition to his homily, Francis recalled meeting a man and his three children during a visit last year to a refugee camp on the Greek island of Lesbos.
The man told the pope that he was a Muslim whose Christian wife was slain before his eyes by "terrorists" after she refused to throw off her crucifix.
Francis did not mention the nationality of the man, and added: "I don't know if [he] was able to leave that concentration camp."
The pope led the service in St Bartholomew Basilica wearing a crimson stola that once belonged to Ragheed Aziz Ganni, a Chaldean priest killed in Mosul, Iraq, in 2007.
Francis called martyrs "the living blood of the Church."
Before his homily, friends and relatives of slain Christians - including the sister of Father Jacques Hamel, an 86-year-old priest killed in France last year in an Islamist attack - spoke before a packed congregation.
The service was held in the run up to Francis' April 28-29 visit to Egypt, a country where Christians are under threat. Earlier this month, at least 45 people were killed following an attack on two Coptic Churches claimed by the Islamic State terror militia.