The parents of US student Otto Warmbier have ramped up their efforts to collect a multimillion-dollar judgment from North Korea over the death of their son.
The parents of Otto Warmbier have filed a claim for a seized North Korean cargo ship in a bid to collect a multimillion-dollar judgment in the US college student's death.
Lawyers for the Warmbiers said in a court filing on Wednesday they have a right to the assets after North Korea failed to respond to their wrongful death claim.
The Warmbiers say their son was tortured after being convicted of trying to steal a propaganda poster and imprisoned for months.
He died days after being returned to the US in a vegetative state in 2017.
A US judge has ordered North Korea to pay more than $US500 million ($A716 million) in the Warmbiers' wrongful death suit.
North Korea has denied mistreating Warmbier.
The US seized the cargo ship in May because it was carrying coal in violation of UN sanctions.