Lohan is embarking on a number of more serious roles

Bobby, showing in competition at the Venice Film Festival, centres on the assassination of Senator Robert Kennedy in Los Angeles in June 1968.

Mean Girls star Lohan, 20, said she hoped people would be stirred by the depiction of Kennedy in the film.

"For people of my generation, I think it's important to bring awareness of a great leader," she said.

'Politically engaged'

Lohan is one of a large number of Hollywood stars who appear in the film, which shows the assassination from the points of view of 22 people either staying or working in the Ambassador Hotel where Kennedy was shot.

The cast includes Sharon Stone, Sir Anthony Hopkins, Martin Sheen and Demi Moore.

Lohan plays a young bride who is marrying the brother of her boyfriend so that he does not have to fight in the Vietnam war.

Lohan arrived with co-star Freddy Rodriguez (left) and Estevez

"I feel I have always been somewhat politically engaged," she said.

"I strongly encourage people of my age and generation to have a say and to vote, and to involve themselves in what's going on in the world, because they are living in it.

"I've always been like that but I keep it to myself. It's safer that way."

The actress, who made her name in a number of teen comedies, has come under scrutiny recently following media reports about her behaviour on set.

Last month, Bobby co-star William H Macy reportedly said her lack of punctuality on set was "disrespectful" to the cast and crew.

But director and former Brat Pack star Emilio Estevez, speaking ahead of the film's premiere in Venice, praised Lohan's "authority" in her role.

"She really dug into it and was so committed," he said.