US director Julian Schnabel has hit out at calls to boycott Scottish actor Gerard Butler who has been targeted by activists for his alleged previous support for the Israeli military.

Butler gives a gripping performance as a hit man in Schnabel's latest film -- "In The Hand of Dante" -- which premieres at the Venice Film Festival on Wednesday.

"It's unfortunate," Schnabel told AFP of the boycott calls by activist group Venice4Palestine which has cited Butler's appearance at a fund-raising event for the Israeli military in 2018.

"It's not even true," the artist and director of Oscar-nominated "The Diving Bell and the Butterfly" added.

"He went to a cocktail party with somebody and happened to have his picture taken. He didn't raise that dough for them."

Butler ("How To Train Your Dragon", "300") was one of several stars to attend a 2018 Hollywood gala organised by the Friends of the Israel Defense Forces (FIDF), which raised a record $60 million, according to a Variety report at the time.

Other attendees included actor Ashton Kutcher and musician and Louis Vuitton menswear head Pharrell Williams, who provided entertainment.

Venice4Palestine, a collective of independent Italian filmmakers, had called on organisers of the Venice festival to disinvite Butler as well as Israeli actor Gal Gadot, who also stars in "In The Hand of Dante".

Schnabel, who is Jewish and a critic of the Gaza war, told AFP that Butler had given the "performance of his life" in his movie about the theft of the original manuscript of Dante Alighieri's "Divine Comedy".

The Venice Film Festival has ruled out disinviting actors -- Butler and Gadot were not expected this year in any case -- but Venice4Palestine co-founder and director Fabiomassimo Lozzi has defended the boycott call.

"I believe that it's justified in the same way I believed about 40 years ago that it was justified boycotting artists who performed in South Africa at the height of the apartheid system," he told AFP.

Israeli TV writer Hagai Levi ("Scenes From a Marriage"), another outspoken critic of the Gaza war, told AFP in Venice that any boycotts had to be targeted.

"Ninety percent of the artistic community in Israel" was against the war, he said.

"Boycotting them is actually weakening the only people who can make a change, or those who are at least fighting," he told AFP on Tuesday.