At a press conference Tuesday, Clooney called for "an open discussion" on the fate of the ancient friezes, which were taken by British diplomat Lord Elgin 200 years ago.
Both the Vatican and the J. Paul Getty Museum had sent parts back, Clooney said, raising the question "of whether or not one piece of art should be, as best as possible, put back together."
"There are certain pieces that you look at and think, that actually is probably the right thing to do," Clooney said.
The fate of the marbles, originally part of the Parthenon temple, is a longstanding issue between Britain and Greece. Greece calls them looted art, and wants all the friezes reunited in a museum in Athens. The British Museum says the marbles "are a part of the world's shared heritage and transcend political boundaries." and are best displayed in London, where the public can view them for free.
Clooney, who directed and stars in "The Monuments Men," said he hadn't meant to spark a storm when he answered a question from a Greek journalist about the marbles at the Berlin Film Festival last week. And he said he'd been told that, as an American, he couldn't understand the issues.
"That can't always be the British default setting," co-star Matt Damon told British reporters, half-joking. "That's not actually an argument, to say 'Well you're American.'"
Bill Murray, another star of the movie, had a firmer opinion on the ancient artwork.
"It's had a very nice stay here, certainly," Murray said. "But London's gotten crowded. There's plenty of room back there in Greece."
"The Monuments Men" tells the true story of a unit of Allied architects, artists, curators and museum directors sent into Europe to prevent art treasures being destroyed or looted by the Nazis.
Adapted from a nonfiction book by Robert Edsel, the film has been criticized for changing names and details. The family of British historian Ronald Balfour, one of two monuments men killed during the war, expressed disappointment that he does not appear in the film. The only British character, played by "Downton Abbey" star Hugh Bonneville, is an alcoholic academic in search of redemption.
"We didn't want to give any of these real men flaws that would be in any way upsetting to their families," Clooney said. "We just wanted the ability to tell a story without offending anyone."
That desire to avoid offense may be one reason the movie - which features a starry international cast including John Goodman, Jean Dujardin and Cate Blanchett - has been called dull and dutiful by some critics.
At its heart, though, the story is gripping. Journalists were reminded of that by the presence at Tuesday's news conference of Harry Ettlinger, one of the few surviving monuments men.
Ettlinger fled Nazi Germany with his family in 1938, and, as a 19-year-old U.S. soldier, was attached to the unit in 1945 because he could speak German. He's the inspiration for a character played by Dimitri Leonidas in the movie.
One question the film asks is: Can saving art be worth a human life?
"Art needs to be around us to make life more meaningful, more enjoyable," Ettlinger said. "We would not like life with white walls around it."