Three American Christians held in North Korea in recent years have been released and are currently flying back to the US with Secretary of State Mike Pompeo, Donald Trump has announced.

The US president confirmed the release of Kim Dong-chul, Kim Sang-duk and Kim Hak-song on Twitter, writing: 'I am pleased to inform you that Secretary of State Mike Pompeo is in the air and on his way back from North Korea with the 3 wonderful gentlemen that everyone is looking so forward to meeting. They seem to be in good health. Also, good meeting with Kim Jong Un. Date & Place set.'

I am pleased to inform you that Secretary of State Mike Pompeo is in the air and on his way back from North Korea with the 3 wonderful gentlemen that everyone is looking so forward to meeting. They seem to be in good health. Also, good meeting with Kim Jong Un. Date & Place set.

— Donald J. Trump (@realDonaldTrump) May 9, 2018

A few minutes later, Trump added: 'Secretary Pompeo and his "guests" will be landing at Andrews Air Force Base at 2:00 A.M. in the morning. I will be there to greet them. Very exciting!'

The news comes after CBN News last week cited sources inside the US Department of Defense as saying that the Christians were all moved from a labour camp early last month and are being given health care and resting.

And it follows a second surprise visit to North Korea from Pompeo to finalise plans for a historic summit between Donald Trump and Kim Jong-un.

The Secretary of State, who first travelled to North Korea as CIA chief in early April, is only the second sitting US secretary of state to visit the country. He arrived in Pyongyang early today, but downplayed the chances of the prisoners being released, saying earlier today that 'there are many challenges along the way'.

Trump previously tweeted about the Christians' potential release last week, 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 this month or next.

'We heard it through our sources in North Korea late last month,' said Choi Sung-ryong, a leading activist, last week. '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 last 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.

'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.

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