The parents of a US student who died days after his release from a North Korean prison are suing Pyongyang.

Otto Warmbier was arrested in January 2016 for stealing a propaganda sign.

North Korea has denied mistreating the 22-year-old student, but his parents insist that his death in July 2017 was the consequence of torture.

The lawsuit comes at a key moment for US-North Korean relations, ahead of a planned meeting between the two countries’ leaders in the coming weeks.

The wrongful-death suit was filed in a federal court in Washington DC. Mr Warmbier’s parents are seeking damages over what they describe as “the hostage taking, illegal detention, torture and killing” of their son.

They say that he was forced to make a false confession before being “brutally tortured and murdered”.

Although foreign countries are usually protected from lawsuits in US courts by sovereign immunity, this does not apply in cases of state-sponsored terrorism.

US President Donald Trump re-designated North Korea a state sponsor of terrorism in November, nine years after it was removed from the list.

However, North Korea has not paid damages awarded in previous cases heard in US courts.

What happened to Otto Warmbier?

Mr Warmbier, an economics student at the University of Virginia, was visiting North Korea on a five-day tour when he was arrested at Pyongyang airport in January 2016.

He was accused of stealing a sign from the hotel where he and fellow students had been staying in the capital, and sentenced to 15 years’ hard labour.

By the time he returned to the US after 17 months in detention, Mr Warmbier was comatose and suffered from brain damage.

North Korea says he fell into a coma after contracting botulism and taking a sleeping pill.

US doctors found no evidence of botulism and said that the student had suffered a “severe neurological injury”, probably caused by a cardiopulmonary arrest.

How did this affect ties US-North Korean relations?

At the time, US President Donald Trump blamed North Korea’s “brutal regime” for Mr Warmbier’s death.

But diplomatic contact between Washington and Pyongyang has since reached its highest level in over a decade,.

Earlier this month CIA director Mike Pompeo secretly met North Korean leader Kim Jong Un in North Korea.

On Friday, Mr Kim became the first North Korean leader to set foot in South Korea since the end of the Korean War in 1953.

He is due to meet President Trump in the coming weeks.