'Kingsley will steal Iron Man 3' says Downey Jr

Robert Downey Jr has been busy talking up Sir Ben Kingsley's role in 'Iron Man 3'.

The revered Brit actor plays sinister villain The Mandarin in the forthcoming sequel, though details of the plot are being kept under wraps.

[Related story: Tony Stark 'has post-traumatic stress' in Iron Man 3]

"Sir Ben is probably going to steal the movie,” Downey Jr told Entertainment Weekly. “There are a lot of contenders who may, but right now he's probably at the top of that list.”

He added that it was Kingsley's improvisation which really impressed.

“He came in as, obviously - speaking of training - as such a technically proficient instrument,” he said.

“And then what proceeded to happen was the release of more vintage, old-school Favreau [improv] stuff with a [screenwriter] Shane Black twist on it. It was kind of frightening to witness, I'll tell you that much.”

The pair also bonded over having worked with directing legend Sir Richard Attenborough.

“We hadn't worked together so we shared only Lord Attenborough, and yeah, of course, there was a connection. We took some pictures together to send Dickie, which must be the strangest visual for him to see - the two of us playing the bad guy and the good guy.”

Kingsley and Downey Jr star alongside Guy Pearce as scientist Aldrich Killian, and Don Cheadle and Gwyneth Paltrow reprising roles as Col. James Rhodes and Pepper Potts.

It's out on April 26, a week before its US release.