Singer Selena Gomez says her kidneys were "done" when she had the transplant operation, and credits her best friend for saving her life.

In an interview with "The Today Show", the pop star, who has battled with autoimmune condition lupus, said it got to the point where it was "kind of life or death", reports mirror.co.uk.

Earlier this year, Selena, 25, revealed that her friend Francia Raisa had donated one of her kidneys to her in a secret operation.

In their first joint interview since the surgery, Gomez said: "My kidneys were just done."

She added: "That was it and I didn't want to ask a single person in my life and that was the day I came home when I found out and she volunteered and did it."

Asked: "You feel like Francia saved your life?", the singer responded: "Because she did. That's it."

Gomez revealed the news of her operation on September 14 by sharing a photograph on Instagram of her and Raisa lying side-by-side in their hospital beds holding hands.

She wrote: "I'm very aware some of my fans had noticed I was laying low for part of the summer and questioning why I wasn't promoting my new music, which I was extremely proud of. So I found out I needed to get a kidney transplant due to my Lupus and was recovering. It was what I needed to do for my overall health. I honestly look forward to sharing with you, soon my journey through these past several months as I have always wanted to do with you.

"...There aren't words to describe how I can possibly thank my beautiful friend Francia Raisa. She gave me the ultimate gift and sacrifice by donating her kidney to me."