Former US president Jimmy Carter said he has cancerous tumors on his brain and will begin radiation treatment Thursday.

The 90-year-old Nobel peace laureate told a press conference said the finding of the four melanoma spots stemmed from a procedure in which a tumor was removed from his liver.

"They did an MRI and found that there were four spots of melanoma on my brain," said Carter, in good spirits. "I get my first radiation treatment for the melanoma in my brain this afternoon."