Three American Christians detained in North Korea could be released having reportedly been moved from a labour camp to a hotel on the outskirts of the capital city Pyongyang, according to CBN News.

CBN News cited sources inside the US Department of Defense as saying that Kim Dong-chul, Kim Sang-duk and Kim Hak-song were all moved from a labour camp early last month and are being given health care and resting.

Donald Trump tweeted about their potential release last night, saying: 'As everybody is aware, 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!'

According to activists campaigning on the men's behalf, the move is a goodwill gesture ahead of the planned summit between Trump and North Korea's Kim Jong Un next month.

'We heard it through our sources in North Korea late last month,' said Choi Sung-ryong, a leading activist. 'We believe that Mr Trump can take them back on the day of the US-North Korea summit or he can send an envoy to take them back to the US before the summit.'

Tony Kim, also known by his Korean name Kim Sang Duk, was arrested on April 22 last year, just before boarding a plane for a flight back to the US.

'My father had just finished his semester as a professor in North Korea when he was arrested at the airport,' said Kim's eldest son, Sol, in a YouTube video, posted several months ago.

Kim was a professor at Pyongyang University for Science and Technology (PUST), the country's only privately-run academic institution which is open about its Christian affiliation.

PUST was founded in 2010 by a Korean American evangelical Christian with the goal of helping North Korea's future elite learn the skills to modernise the isolated country and engage with the outside world, according to Reuters.

'My mum, brother and I miss our dad so much,' Kim's son said in the video.

Another Christian professor from PUST, Kim Hak Song, was also arrested a month later.

Both men were arrested on suspicion of alleged 'hostile acts'.

A third individual, a Korean-American missionary named Kim Dong Chul, was arrested in October 2015 and sentenced in March 2016 to 10 years of hard labour for subversion.

Trump's national security adviser, John Bolton, said earlier this week that releasing the three Americans would demonstrate North Korea's sincerity in the run-up to a historic summit.

'If North Korea releases the detained Americans before the North-US summit, it will be an opportunity to demonstrate their authenticity,' Bolton told Fox News.

Trump confirmed last week that his administration was in high-level talks to secure the release of the Americans.

'We are likewise fighting very diligently to get the three American citizens back,' Trump told a press conference last month with the Japanese prime minister Shinzo Abe. 'I think there's a good chance of doing it. We're having very good dialogue,' he added.

The US Secretary of State Mike Pompeo also reportedly raised the plight of the Christians when he secretly met with North Korea's leader Kim Jong Un over the Easter weekend.

Trump this week said he will soon announce a location and date for his meeting with North Korea's dictator.

'We're setting up meetings right now and I think it's probably going to be announced over the next couple of days, location, and date,' Trump told reporters at the White House on Tuesday.

The two leaders are expected to discuss North Korea's promise to end its nuclear testing and eventually give up its atomic weapons.

'The main thing, we want to get peace,' Trump said. 'It was a big problem, and I think it's going to work out.'