Simpson (left) and Leto
John Spellman/Retna; Trent Warner/startraks
"They're an item," a source close to Leto tells PEOPLE in its new issue.
The actor, 34 – who has dated Cameron Diaz and Scarlett Johansson – chatted up Simpson and then scored her number on June 2 at the Los Angeles nightclub Hyde.
Four nights later, Leto partied solo at New York City's club Plumm, then headed to Double Seven, where he met up with Simpson, 25. "They were hanging all over each other," says a witness.
Still, a source close to Simpson tells PEOPLE, "Jessica is not dating anyone," and the singer's rep insists, "She is single." Adds Leto's rep, "There is no truth to these rumors."
But what about Lindsay Lohan, who was linked with Leto, her costar in the upcoming Chapter 27, last year (and who clashed with Simpson in April over the attentions of mutual pal Brett Ratner)? "She's telling friends she's furious," says a source close to the actress. "She feels betrayed by Jared."
Says Lohan's rep, "Lindsay could care less."
