Celebrities of Armenian descent including Cher and the Kardashians lent their support this week to "The Promise," a period drama centred around the massacre of Christian Armenians during World War One in what is now Turkey.

"The Promise," out in U.S. theatres on April 21, stars Oscar Isaac as an Armenian medical student and Christian Bale as an American foreign correspondent, both of whom fall in love with the same woman.

Their love triangle unfolds as the Ottoman Empire's entry into the war is followed by the 1915 massacre of Christian Armenians.

"So many people, when confronted with a period film, they tend to ask that question 'why is this still relevant?'" Bale told Reuters at Wednesday's red carpet premiere in Los Angeles.

"You only have to look at the news to see sadly how relevant this story still is," he added.

Terry George, who directed 2004 Oscar-nominated historical drama "Hotel Rwanda," said shooting "The Promise" coincided with news of Yazidi refugees besieged by Islamic militants in northern Iraq and the mass exodus of Syrians attempting to flee the war-torn country for Europe.

"As we were shooting, we were watching the same events in the same location - people under siege in the mountains and drowning in the Mediterranean," George said.

The nature and scale of the massacre of Christian Armenians remains a contentious issue.

Turkey accepts that many Armenians died in partisan fighting beginning in 1915, but denies that up to 1.5 million were killed and that this constituted an act of genocide, a term used by many Western historians and foreign parliaments.

Singer Cher, whose father was Armenian-American, joined reality TV stars Kim and Kourtney Kardashian at the premiere.

"There is something about people when they don't see other people as human beings, then they objectify and then they can do anything to them," Cher said about the massacre.

"Westworld" actress Angela Sarafyan, who plays Isaac's wife in the film and is of Armenian descent, described the role as very personal.

"My great-great-grandparents fled to Syria, Aleppo to survive and to start a family and today, people from Syria, Aleppo leave to other places so they can live," she said.

"One hundred years have gone by and that is still happening," she added.