Washington, Aug 20 (IANS): Former US president Jimmy Carter on Thursday said his cancer had already spread to his brain.

Speaking at a press conference for the first time since he announced his cancer diagnosis on August 12, Carter said he has four small spots of melanoma on his brain and his radiation treatment would start later Thursday.

So far, the pain was "very slight", Carter was quoted as saying by Xinhua. He added that he was not feeling any weakness or debility.

He underwent surgery on August 3 to remove a tumour found on his liver, and had once thought that the cancer was confined to his liver. However, an MRI soon found that cancer had already spread to his brain.

"I just thought I had a few weeks left, but I was surprisingly at ease," said Carter, adding that cancer had so far been found only in his liver and brain.

Four family members of Carter, including his father, brother and two sisters, died of pancreatic cancer. Canter said no cancer had been found on his pancreatic so far.

Doctors still had not been able to find out where the cancer on his brain originated.

Carter said he never considered not fighting the cancer because he has full faith in his doctors, and he chose to "hope for the best and accept what comes."

Carter's health has been closely watched this year. He cut short an election monitoring trip to Guyana in May after falling ill.

Carter, born in 1924, served as the 39th US president from 1977 to 1981. He was awarded the Nobel Peace Prize in 2002.