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 tie Lee and Ling's release with talks over the North Korean nuclear programmes.

Pyongyang withdrew from the six-nation nuclear 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 been stalled months before then.

North Korea has received another former president of the US. Jimmy Carter visited in 1994, again as nuclear tensions with North Korea were rising. He met then-leader Kim Il Sung, father of the current leader. Their meeting brought the North back to the negotiating table.

Clinton's visit caused hopes to rise 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 who has also been detained in the North since March when he was arrested for allegedly criticising its totalitarian regime.

North Korea has also remained silent on the fate of a South Korean fishing boat after claiming at the weekend that the boat had illegally intruded into its territory.

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