Former US president Jimmy Carter is planning to visit North Korea soon on a mission to secure the release of an American man serving eight years of hard labor there, Foreign Policy magazine has said.

"Jimmy Carter is set to travel to North Korea very soon, according to two sources familiar with the former president's plans, in what they characterized as a private mission to free a US citizen imprisoned there," the magazine said.

The Nobel Peace Prize laureate is planning to leave "within days," it said.

The United States has repeatedly voiced concern about the health of Aijalon Mahli Gomes, who was jailed for illegally crossing the country's border with China.

Gomes, a 30-year-old former English teacher in South Korea and reportedly a devout Christian, was arrested in January. He was sentenced in April and fined the equivalent of 700,000 dollars.

North Korea state media said in July that Gomes tried to commit suicide and was being treated in hospital.

Gomes was "driven by his strong guilty conscience, disappointment and despair at the US government that has not taken any measure for his freedom," the communist state's official news agency said.

The Foreign Policy report said that Carter would be traveling as a private citizen, similar to the mission carried out by Bill Clinton last year when he secured the release of Current TV reporters Laura Ling and Euna Lee, who were also jailed after wandering across the North Korean border with China.

Asked earlier in the day about the potential for a trip by Carter to North Korea, State Department spokesman Philip Crowley told AFP: "I have nothing I can share with you."