Hartnett and Sienna begin dating?

Josh Hartnett and Sienna Miller have sparked rumours after being spotted together in a hotel in Los Angeles.

The Black Hawk Down star, who recently split with girlfriend Scarlet Johansson, was spotted with Miller at the Chateau Marmont hotel.

A source told The Sun, "They sat side-by-side on a couch laughing and chatting for about and hour.

"They were then joined by a girlfriend of Sienna's but carried on with their flirting"

Miller, who appears in the upcoming film Factory Girl as Andy Warhol's muse, has been linked with a host of stars, including Daniel Craig, Leonardo Di Caprio and Orlando Bloom.

Her spokesperson however claimed that she and Hartnett were "just friends".