MIAMI, US (AFP) - Former US president Jimmy Carter underwent surgery on his liver on Monday to have a small mass removed, his Atlanta-based Carter Center said.

The operation on Mr Carter, 90, was carried out at Emory University Hospital in Atlanta, a hospital statement said.

"His operation proceeded without issues, and the prognosis is excellent for a full recovery," it added.

Carter, who was in the White House from 1977 to 1981, has been an extremely active ex-president, volunteering, working as an elections monitor and lobbying for health campaigns via his charitable foundation in the developing world.

In May, Mr Carter cut short a trip to Guyana after he fell ill. He was flown back to Atlanta, where the next day he attended an event at The Carter Center, which he founded in 1982.