A US court has ordered Pyongyang to pay $US501 million ($710 million) in damages for the torture and death of US college student Otto Wambier, who died last year shortly after being released from a North Korea prison.

Mr Warmbier’s parents sued North Korea in April over their son’s death. The 22-year-old student died in the US days after being released from captivity in a coma. An Ohio coroner said the cause of death was lack of oxygen and blood to the brain.

“North Korea is liable for the torture, hostage taking, and extrajudicial killing of Otto Warmbier, and the injuries to his mother and father, Fred and Cindy Warmbier,” Judge Beryl Howell of the US District Court for the District of Columbia said.

Pyongyang blamed botulism and ingestion of a sleeping pill for Mr Warmbier’s death and dismissed torture claims.

Fred and Cindy Warmbier said they were thankful that that the court found the government of Kim Jong-un “legally and morally” responsible for their son’s death.

Otto Warmbier, 22, died days after his release from North Korea. Photo: Getty

“We put ourselves and our family through the ordeal of a lawsuit and public trial because we promised Otto that we will never rest until we have justice for him,” they said in a joint statement.

“Today’s thoughtful opinion by Chief Judge Howell is a significant step on our journey.”

The lawsuit, filed in April, describes in horrific detail the physical abuse Warmbier endured in North Korean custody.

When his parents boarded a plane to see him upon arrival in the US, they were “stunned to see his condition,” according to court documents.

The 22-year-old was blind and deaf, his arms were curled and mangled and he was jerking violently and howling, completely unresponsive to his family’s attempts to comfort him.

His once straight teeth were misaligned, and he had an unexplained scarred wound on his foot. An expert said in court papers that the injuries suggested he had been tortured with electrocution.

A neurologist later concluded that the college student suffered brain damage, likely from a loss of blood flow to the brain for 5-20 minutes.

The complaint also said Mr Warmbier was pressured to make a televised confession and then convicted of subversion after a one-hour trial. He was denied communication with his family.

In June 2017, Mr Warmbier’s parents were informed he was in a coma and had been in that condition for one year.

US President Donald Trump tweeted that he was looking forward to another summit with North Korea.

“Christmas Eve briefing with my team working on North Korea – Progress being made. Looking forward to my next summit with Chairman Kim!” he said, with a photo showing him reading papers at his White House desk with advisers nearby.