U.S. President Donald Trump on Thursday hinted at the possibility of the release of three U.S. detainees in North Korea.
"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!" Trump tweeted.
His message came amid a report that North Korea has relocated three American detainees from a labor camp to a hotel on the outskirts of Pyongyang ahead of a planned summit between leader Kim Jong-un and Trump.
The U.S. citizens -- Kim Hak-song, Tony Kim and Kim Dong-chul -- were moved in early April following instructions from superior authorities, it said. They have been accused of espionage or "hostile acts" against the regime.
North Korea's detention of foreigners has drawn sharp criticism, especially after Otto Warmbier, a U.S. college student, died last year shortly after being sent home from Pyongyang in a coma following a 17-month detention.
The U.S. and the North are believed to be in talks over the potential release of the three. North Korea has used detained Americans as leverage to force the U.S. to open bilateral talks with it in the past.
Trump and Kim are expected to hold an unprecedented summit, probably this month, after the North's ruler and President Moon Jae-in met for a summit on Friday at the border village of Panmunjom.
Former U.S. President Bill Clinton visited the North in August 2009 in a private capacity to bring home two American journalists detained in the country.
Another ex-U.S. president, Jimmy Carter, also made a trip to Pyongyang in August 2010 to win the release of Aijalon Mahli Gomes, a U.S. citizen who was detained in the communist country for about seven months.
James R. Clapper, former director of National Intelligence, made a secret visit to the North in November 2014 to bring home two detained Americans, Kenneth Bae and Matthew Miller.
Former top U.S. nuclear envoy Joseph Yun visited Pyongyang in June last year to win the release of Warmbier.
Meanwhile, North Korea is currently holding six South Koreans -- three of whom are pastors -- on charges of committing what the North called anti-North Korea crimes.
"The government is making efforts to resolve the humanitarian issue," said an official at South Korea's unification ministry, when asked about Seoul's efforts to free the South Korean detainees.