WASHINGTON (AFP/REUTERS) - Former US president Jimmy Carter on Wednesday said that recent liver surgery had shown he has cancer.

The 39th president, now aged 90, underwent an operation deemed successful earlier this month, to remove a "small mass".

"That procedure revealed that I have cancer that now is in other parts of my body," he said in a brief written statement Wednesday.

"I will be rearranging my schedule as necessary so I can undergo treatment.

"A more complete public statement will be made when facts are known, possibly next week," said the Nobel Peace Prize winner, whose two sisters, brother and father all died from pancreatic cancer.

The Georgia native will be treated at Emory University Hospital in Atlanta.

Carter, a Democrat, served as the 39th president from 1977 to 1981 after defeating Republican incumbent Gerald Ford.

He was defeated for re-election in 1980 by Republican Ronald Reagan.

The Carter Centre in Atlanta said last week that he had undergone elective surgery at Emory University Hospital to remove a small mass in his liver.

It added that the operation had proceeded without issues and that the prognosis was excellent for a full recovery.

Carter cut short a trip to Guyana in May after feeling unwell and returned to Georgia, where he served as governor and a state senator.

He had travelled to the South American country to observe national elections.

At the time, the centre said only that Carter had departed after "not feeling well."

Republican Georgia Governor Nathan Deal and his wife issued a statement saying Carter was "in their prayers as he goes through treatment."

News of his illness prompted a groundswell of people wishing him well.

Carter received words of sympathy and encouragement via Twitter from former CNN host Larry King: "We go back many years. Stay strong Mr President."

"We hope for his full recovery and return to his inspiring work," said Apple CEO Tim Cook.

"Dems across the country are pulling for you," said Democratic National Committee chairwoman Debbie Wasserman Schultz.

There are four former US presidents alive today: Carter, George H. W. Bush, Bill Clinton and George W. Bush.

A Nobel Peace Prize winner and activist on a range of issues from global democracy to women and children's rights, as well as affordable housing, Carter published his latest book last month, entitled A Full Life: Reflections At Ninety.

In July, he gave a wide-ranging interview to Reuters editor-at-large Harold Evans on his life from his childhood on a Georgia peanut farm to his presidency.

Carter recalled growing up in a home without running water or electricity, at a time when he said the daily wage was US$1 for a man, 75 cents for a woman, and a loaf of bread cost 5 cents.

He said the civil rights movement led to important progress towards racial equality in the United States, but lamented "there's still a great prejudice in police forces against black people and obviously some remnants of extreme racism".

Carter was recipient of the 2002 Nobel Peace Prize for his tireless efforts to promote social and economic justice.