Robert Downey Jr to wear Iron Man suit again

Robert Downey Jr is reportedly close to signing on to reprise his role as Iron Man in Captain America 3.

Robert Downey Jr may don the Iron Man suit again to go head-to-head with Captain America in an upcoming Marvel movie.

Downey Jr is reportedly in final negotiations to sign onto Captain America 3, according to Variety, which would kick off a new phase in the Marvel Cinematic Universe.

The industry bible says the move is significant because Captain America 3 will introduce the Civil War storyline from Marvel's comic books, which pits Tony Stark's Iron Man against his Avengers ally, Captain America aka super soldier Steve Rogers (played by Chris Evans).

In the plot, the pair are at loggerheads over the Superhero Registration Act - a program that forces people with superhuman abilities to reveal themselves to the US government and act under their command.

According to Variety, there were complications, because Marvel originally intended for Downey Jr's part to be small, but the actor wanted something more substantial.

Marvel boss Kevin Feige fought for Downey Jr to return, because the Civil War storyline could have a big impact on Avengers 4, as well as new characters such as Doctor Strange and Ant-Man.

Downey Jr, named the world's highest paid actor for the second year in a row in 2014, will reportedly earn around $40 million for Captain America 3, and will be paid an additional sum if it outperforms Captain America: The Winter Soldier at the box office.

Captain America 3 is set to begin production next year for a May 6, 2016, release.

Downey Jr will next be seen as Iron Man in the highly anticipated Avengers: Age of Ultron, which releases in cinemas on April 23.