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."