Pyongyang is reportedly seeking direct talks with Washington, while the US wants to continue six-nation negotiations that also involve China, South Korea, Japan and Russia with the aim of ending North Korea's nuclear weapons programme.

Kim Yong Hyeon, a professor of North Korean studies at South Korea's Dongguk University, said the 42nd president's visit might be the best chance for North Korea to take negotiations with the US to a higher level.

'Besides, Kim may prove to the world that he is well enough to meet a US official,' professor Kim said.

Lee and Ling were arrested in mid-March on the Chinese-North Korean border while working on a story about North Koreans fleeing their impoverished country. They were working for the US-based online broadcaster Current TV, which was co-founded by Al Gore, who served as vice president under Clinton.

Yonhap quoted a source in Seoul as saying the US and North Korea had been in 'active consultations' in recent weeks about Lee and Ling.

The US government, now headed by Clinton's fellow Democrat President Barack Obama, has refused to link Lee and Ling's release with talks over the North Korean nuclear programme. The White House denied a Yonhap report the Clinton was carrying a specific message from Obama.

Pyongyang withdrew from the six-party talks after being internationally condemned for launching a long-range rocket in April and conducting its second nuclear test in May, but the negotiations had stalled months earlier.

Clinton's visit prompted hope for the release of the US journalists at a time of uncertainty about the fate of a South Korean manager at a jointly run North-South industrial park. He was arrested in March for allegedly criticising the totalitarian regime.

North Korea has also remained silent on the fate of a South Korean fishing boat after claiming at the weekend that the vessel had violated its territorial waters.

The fishing boat with four crew members aboard is believed to have accidently strayed into North Korea waters last week because of a malfunction of its global positioning system.