Actor-turned-humanitarian George Clooney met with British Prime Minister Gordon Brown on Tuesday to discuss the Sudan genocide crisis.

The Oscar winner visited Brown's official residence in London's Downing Street in his capacity as a United Nations Messenger Of Peace, a post to which he was appointed in January this year.

Brown said: "I am grateful for the leadership George Clooney has shown in drawing attention to this crisis - this is a humanitarian tragedy of colossal proportions and the world must take note and act.

"The U.K. is working with the international community and others to pressure all sides to agree a ceasefire and start peace talks."

Clooney has become a leading celebrity advocate for action against genocide in the Darfur region of Sudan after filming a documentary about the ongoing violence and refugee crisis there last year.