British actress Sienna Miller has brushed off romance rumours linking her to Brad Pitt, branding the reports "predictable and silly".

The American Sniper beauty was recently spotted attending a group dinner in Los Angeles, where Brad was also among the guests, and sources claimed the pair was caught doing some "serious flirting".

One insider told the New York Post's Page Six gossip column Brad and Sienna were "heavily enjoying each other's company", but the actress has dismissed the claims, insisting there is no truth to the speculation.

"I'm not going to even dignify it with a response," the actress remarked to Page Six when quizzed about the reports while promoting her new film, The Lost City of Z, which Brad executive produced.

"It's predictable and silly," she added.

Brad, 53, has been single since splitting from his wife Angelina Jolie in September (16), while Sienna, 35, reportedly struck up a relationship with her Foxcatcher director Bennett Miller last year (16).

She has also remained close to her former fiance, fellow actor Tom Sturridge, since calling off their engagement in 2015.

The exes are parents to four-year-old daughter Marlowe, and Sienna recently told Harper's Bazaar magazine she still has strong feelings for Tom.

"We still love each other," she told the publication earlier this year (17). "I think in a break-up somebody has to be a little bit cruel in order for it to be traditional, but it’s not been acrimonious in a way where you would choose to not be around that person."