The girl in the picture, Phan Thi Kim Phuc, now 59, also was at the pontiff’s general audience in St. Peter’s Square and both chatted with him for a few minutes.

Ut, 71, who as working for the Associated Press at the time, won numerous awards for the photo, called “The Terror of War” but sometimes referred to as the “Napalm Girl”. They included the 1973 Pulitzer Prize.

The attack near Kim Phuc’s village led to the girl’s tearing off her burning clothes and ran. Ut and other photographers took her to a hospital.

The photo ran on the front pages of many newspapers in the United States, and its brutal imagery became a powerful force in the anti-war movement around the world.

Audio tapes of White House conversations released in 2002 by the U.S. National Archives and Records Administration revealed that then-President Richard Nixon was so concerned about the effect the photo could have against the war in Vietnam that he wondered if it was a fake.

Francis opposes all forms of war. In the past, he has given visitors a picture showing a Japanese boy carrying his dead brother after the atomic bomb blast at Nagasaki in 1945.

Kim Phuc moved to Canada after the war and is now a UNESCO ambassador.

Ut moved to Los Angeles and became a Hollywood photographer.

She and Ut are in Italy for an exhibition of his pictures called “From Hell to Hollywood”.