Schindler's List star Ralph Fiennes was among the signatories of the petition, which began circulating during the buildup to the Cannes Film Festival.
Signatories also include Juliette Binoche, who is chairing the jury at Cannes, Rooney Mara, Jonathan Glazer, US indie director Jim Jarmusch, Lupin star Omar Sy, Richard Gere, Susan Sarandon, Pedro Almodovar and Mark Ruffalo.
The initiative, called "Artists for Fatem", was sparked by the killing of Palestinian photojournalist Fatima ("Fatem") Hassouna, who was the subject of a documentary that premiered at Cannes.
Hassouna, 25, was killed in an Israeli air strike along with 10 relatives in her family home in northern Gaza last month, the day after the documentary was announced as part of the ACID Cannes selection.
"As artists and cultural players, we cannot remain silent while genocide is taking place in Gaza and this unspeakable news is hitting our communities hard," the open letter says.
Middle East Eye