Viggo Mortensen and Caleb Landry Jones are to lead the cast of the Vietnam War film 'Two Wolves'.

The duo have boarded the movie that is being directed by Alex Gibney – who is best known for documentaries such as 'Taxi to the Dark Side' and 'Going Clear'.

An official description for the picture reads: "The film tells the story of helicopter pilot Hugh Thompson who, during the Vietnam War, turned against his fellow soldiers to halt the massacre of unarmed civilians in the village of My Lai, and rescued survivors of the atrocities.

"But far from being treated as a hero, Thompson was branded a traitor and threatened with court-martial, while the actual perpetrators of the war crimes were lionised by supporters and pardoned by President Nixon.

"It came down to General William 'Ray' Peers to investigate what really happened at My Lai and to corroborate the truth of Hugh Thompson's story... a truth for which both men were willing to fight despite the enormous risk to themselves."

'Two Wolves' has been written by double Oscar winner Anthony McCarten and Matt Cook. Paul Higgins, Peter Saraf and Will Clarke are all producing the flick.

Gibney said: "This is a film I have wanted to make for seven years.

"Now that I have the right team in place, we can tell this powerful tale. It's a true story about how everyday people can become heroes, not through supernatural powers, but through a commitment to do the right thing in the worst possible circumstances.

"Since 'Enron', I've been making films about people who abuse their power. This is a film about two men who fought back."

Higgins added: "The message of 'Two Wolves' is a powerful one. It implores us to consider the importance of the right leaders; the importance of the truth; the importance of learning from our mistakes or being forever destined to repeat them.

"It explores the need to listen to the better angels of our nature and, the notion that one man can make a difference. There has never been a more pertinent time for this story to be told."