Jennifer Lawrence -- Backstage at iHeartRadio Festival During Coldplay Gig

Rumors of a relationship between Jennifer Lawrence and Coldplay singer Chris Martin have been swirling for weeks ... and now, the Oscar winning actress is throwing fuel on the fire.

Lawrence was spotted backstage at the iHeartRadio Music Festival Friday night in Las Vegas ... the same festival where Coldplay was performing.

Still no official confirmation they're dating ... but Martin and Gwyneth Paltrow split up back in May. Lawrence and her ex-boyfriend Nicholas Hoult broke up in August.