North Korea is in talks with the United States and Sweden to release three jailed Americans as part of increased diplomatic activity ahead of Pyongyang's planned summits with Washington and Seoul.

The release of the three Korean-Americans is under discussion through multiple channels more than a week after President Donald Trump agreed to meet the North's Kim Jong Un, according to several media reports.

Pyongyang has yet to confirm it even made the US summit offer - relayed by Seoul envoys who had met Kim in Pyongyang - but South Korea said he had given his word about his commitment to denuclearisation.

Mr Trump's stunning announcement has triggered a race to set a credible agenda for what would be historic talks between the two leaders.

Seoul-based MBC TV station reported on Sunday that Pyongyang and Washington had "practically reached" a final agreement on the release of US citizens Kim Hak-song, Kim Sang-duk and Kim Dong-chul. "They are hammering out details over the timing of the release," it quoted a South Korean diplomatic source as saying.

The negotiation was held through the North's mission to the United Nations and the US State Department -- an unofficial avenue of communication dubbed the "New York channel", the source said.

CNN said the potential release of the three prisoners was also discussed at three-day talks in Stockholm between the North's Foreign Minister Ri Yong Ho and Swedish counterpart Margot Wallstrom that ended Saturday.

_____________________

North Korea experts fret at Donald Trump's go-it-alone approach to meeting Kim Jong-un

Parents of US student Otto Warmbier call North Korea ‘terrorists’

_____________________

Sweden represents Washington's interests in the North. It raised the issue of American detainees to "move things in the right direction", CNN quoted one source as saying.

Kim Dong-chul, a South Korea-born American pastor, has been detained by the North since 2015 when he was arrested for spying. He was sentenced to 10 years' hard labour in 2016.

Kim Hak-song and Kim Sang-duk -- or Tony Kim -- were both working at the Pyongyang University of Science and Technology, founded by evangelical Christians from overseas, when they were detained last year on suspicion of "hostile acts".

The issue of American detainees has long been contentious but it escalated last year with the death of US student Otto Warmbier.

He was arrested in January 2016 while visiting North Korea and was accused and convicted of removing a propaganda poster from his hotel room. Sentenced to 15 years hard labour he is believed to have fallen ill shortly after but the University of Virginia student’s condition was not discovered until June 2017 when the communist authorities said he had fallen into a coma after being treated for botulism. He died in his home state of Ohio six days after US diplomats had secured his release on medical grounds.

Reports of the possible release of the three US citizens come amid a flurry of diplomatic activities involving Pyongyang, Washington and Seoul.

During a visit to Pyongyang by Seoul's envoys earlier this month, Kim reportedly offered to meet Trump, with the US president subsequently agreeing to talks by May. No specific time or venue has been set.

Mr Kim also agreed to hold a summit with South Korean President Moon Jae-in next month - the third ever between the two Koreas - according to the envoys. And he reportedly offered to consider abandoning his nuclear weapons in exchange for US security guarantees.

South Korean Foreign Minister Kang Kyung-wha said in an interview aired Sunday that Kim was "taking stock" after Trump's surprise decision to accept the invitation, but that a channel of communication had been established.

She said Kim had "given his word" on his commitment to denuclearisation.

"But the significance of his word is quite, quite weighty in the sense that this is the first time that the words came directly from the North Korean supreme leader himself, and that has never been done before," Kang told CBS's "Face the Nation".

Nothing has been offered to the North Koreans to engage in negotiations, she said.

The Stockholm talks overlapped with another meeting between the national security advisers of the US, South Korea and Japan.

US National Security Adviser H.R. McMaster, the South's Chung Eui-yong and Japan's Shotaro Yachi met in San Francisco over the weekend and vowed "close policy coordination" for the weeks ahead, Seoul's presidential office said.

They agreed that peace on the Korean peninsula hinges on the success of the two planned summits, vowing "not to repeat the failure of the past", it said in an apparent reference to previous botched nuclear disarmament negotiations with the North.

Also on Sunday a senior North Korean diplomat arrived in Finland for talks on peninsula issues with former officials and academics from the US and South Korea.

The sudden rapprochement comes months after the North staged its most powerful nuclear test and test-fired missiles capable of reaching the US mainland.

Mr Kim and Mr Trump had previously traded threats of war and personal insults, which heightened global concerns of another conflict on the peninsula once reduced to ruin by the 1950-53 Korean War.