Kristen Stewart - Kristen Stewart's Dakota Restrictions

Kristen Stewart "wasn't allowed to grope" Dakota Fanning on the set of 'The Runaways'.

The actress told how there were strict rules in place when she performed her on-screen kiss with the teenage star, but their intimate moment felt "natural".

Kristen - who rose to fame in the 'Twilight' franchise - said: "Well, she was 15, and I wasn't allowed to grope her. I'm not kidding. There are major restrictions.

"But it's very innocent in the movie, just a kiss. Of course, everyone's talking about it like it's a huge deal but it was so natural and impulsive.

"And it's like five seconds in the movie."

The film tells the true story of rock star Joan Jett - who the 20-year-old actress portrays - and her all-girl band The Runaways, a teenage group from the 70s. Dakota plays the group's singer Cherie Currie.

Kristen said the role differed to her previous work because she had to portray a living person, but that she became close to Joan - who was one of the movie's producers - during filming.

She told Stylist magazine: "I think we really do understand each other, and that's rare. We have a lot of idiosyncrasies and tics that are really different to other people, and so I feel the role was an easy thing to step into.

"When we were shooting I was doing a lot of press and I think I was sort of wearing her and projecting her a little bit."