U.S. President Donald Trump hinted Wednesday that there would be imminent news about three Americans detained in North Korea, after sources said they had been relocated ahead of their possible release. The development comes as Trump is preparing for a historic summit meeting with North Korean leader Kim Jong Un, following months of tense saber-rattling over the North's nuclear and missile programs.

"The past Administration has long been asking for three hostages to be released from a North Korean Labor camp, but to no avail. Stay tuned!" Trump wrote on Twitter.

Two of the three hostages were detained in 2017, after Trump had assumed office.

The United States has been demanding the North free Kim Hak-song, Kim Sang-duk and Kim Dong-chul and reports have said the two sides were close to reaching a deal on their release.

"They are staying in a hotel on the outskirts of Pyongyang," Choi Sung-ryong, a South Korean activist with contacts in the North told AFP earlier, adding the three were being kept separately but "going on tours, receiving medical treatment and eating good food."

Diplomatic sources in Pyongyang have said there were rumors that the three had been relocated, but there had been no confirmation of their exact whereabouts.

A U.S. State Department official could not confirm the reports, but added, "We are working to see U.S. citizens who are detained in North Korea come home as soon as possible."

The matter was discussed when U.S. Secretary of State Mike Pompeo travelled to Pyongyang last month, according to The Wall Street Journal.

And speaking to Fox News on Sunday, U.S. National Security Adviser John Bolton said releasing the hostages would be "an opportunity" for the North to "demonstrate their authenticity."

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

CNN had said the prisoners' release was also discussed at three-day talks in Stockholm between the North's Foreign Minister Ri Yong Ho and Swedish counterpart Margot Wallstrom in March. Sweden represents Washington's interests in the North.