Sienna Miller

Sienna Miller and Josh Hartnett Get Cozy

01/17/2007 at 03:30 PM EST

New couple alert? Sienna Miller and Josh Hartnett certainly seemed cozy at Hollywood's Chateau Marmont on Tuesday night.

Miller, 25, and Hartnett, 28, sat side-by-side on a couch in the hotel restaurant's living room area, laughing and chatting for about an hour before they were joined by a female friend of Miller's.

But they kept things intimate – at one point, Miller stood in front of a seated Hartnett, who held on to her thigh with his hand. The pair eventually headed out, cocktails in hand, to the hotel's poolside bungalow area.

So are the single actors (she split with Jude Law in November; he most recently dated his Black Dahlia costar Scarlett Johansson) an item? "They're friends, just friends," Miller's rep tells PEOPLE. "They were just hanging out."

Seconds a rep for Hartnett: "There is nothing to comment on."