LONDON (AFP) - US actor Sean Penn, who won Oscars for his brooding ex-convict in Mystic River (2003) and a doomed gay rights leader in Milk (2008), turns action hero in The Gunman, a thriller that had its world premiere in London on Feb 16.

Starring alongside Spain's Javier Bardem and Britain's Idris Elba, Penn plays a former assassin whose last job - killing a politician from the Democratic Republic of Congo (DRC) - comes back to haunt him.

The film is based on a novel by Frenchman Jean-Patrick Manchette, and is set in the DRC, as well as Barcelona, London and Gibraltar. It is being released from this week and will be in Singapore theatres in end-March.

With 40 films under his belt, the 54-year-old Penn has not played an action hero since Sydney Pollack's The Interpreter in 2005.

Director Pierre Morel, the Frenchman who turned Liam Neeson into an action heart-throb in Taken (2008) and did the same for John Travolta in From Paris With Love (2010), told AFP he was drawn to making movies that weren't just "action for action's sake".

"I always say, if it's a movie which is driven by action, then I'm interested. A smart story with action in it, then I'm all for it," Morel said.

He praised stars Penn, Bardem and Elba as easy to work with.

"These guys are so talented, they work so hard, that you know that they are going to deliver," Morel said.

Like in No Country for Old Men and Skyfall, Bardem is once again a villain.

He is joined by British actor Mark Rylance, who stars in the new television drama Wolf Hall about the court of king Henry VII.

The female lead is Italian actress Jasmine Trinca.