South Korean President Moon Jae-in on Tuesday condoled the death of a US student who was released by North Korea less than a week ago.

Moon sent a consolation letter to the family of Otto Warmbier, 22, who passed away within days of his release, Xinhua news agency reported.

Moon's spokesman Park Soo-hyun told the media that the President expressed regrets for the US university student's death in the letter sent to the Warmbier family.

The University of Virginia student was held prisoner in North Korea while travelling. 

Warmbier was arrested in January 2016 for allegedly trying to steal an item showing a propaganda slogan, and was sentenced to 15 years of hard labour in March.

Following a series of diplomatic contacts with Washington, Pyongyang released Warmbier, who was in coma.

Moon took the opportunity to urge Pyongyang to return other South Korean and US citizens held there, vowing to make all-out efforts for their release.

Moon's comments came ahead of his 29 June visit to Washington for his first two-day summit meeting with US President Donald Trump.