WASHINGTON — Pope Francis, no stranger to lending his moral authority to a range of causes, made a comparison to the Nazi Holocaust while meeting over the weekend with some migrants at the Basilica of St. Bartholomew in Rome.

According to the BBC, Francis related a story Saturday about a Middle Eastern refugee whose wife was killed by Islamist militants for holding on to her crucifix.

‘‘I don’t know if he managed to leave that concentration camp,’’ the pope said. ‘‘Because many of them are concentration . . . because there is a great number of people left there inside them.’’

The American Jewish Committee, which advocates for Jewish causes, released a statement saying it understood the pontiff’s sentiments but didn’t agree with his comparison.

‘‘The conditions in which migrants are currently living in some European countries may well be difficult, and deserve still greater international attention, but concentration camps they certainly are not,’’ AJC chief executive David Harris said on the group’s website.

‘‘The Nazis and their allies erected and used concentration camps for slave labor and the extermination of millions of people during World War II. There is no comparison to the magnitude of that tragedy.’’

‘‘We respectfully urge the pope to reconsider his regrettable choice of words,’’ Harris added.

According to the Office of the United Nations High Commissioner for Refugees, there are 65.3 million forcibly displaced people across the world. Of the 21.3 million refugees in the world, half are children.

The Calais camp for migrants in northern France, nicknamed ‘‘the Jungle,’’ had cramped makeshift tents, vermin, contaminated water, and many inhabitants suffering from diseases, the Guardian reported.

In Greece, Interior Minister Panagiotis Kouroublis, touring the Idomeni camp on the border with Macedonia, also compared it to a concentration camp. Idomeni was where a photo emerged of two Syrian parents washing their newborn baby, Bayan, in a puddle.

In Jerusalem on Sunday, Prime Minister Benjamin Netanyahu opened Israel’s annual memorial day for the 6 million Jews systematically killed by Nazi Germany and its collaborators by saying the lessons of the Holocaust guide him daily and issuing a warning to Israel’s enemies not to test it.

The Nazis and their collaborators wiped out a third of world Jewry. The state of Israel was established just three years after the end of the war and hundreds of thousands of survivors made their way here.