Fred and Cindy Warmbier, parents of 22 year old Otto Warmbier -- who died days after being sent back to the United States from North Korea in a coma in 2017 -- condemned the US leader's "lavish praise" of Kim this week following their summit in Hanoi.

"We have been respectful during this summit process. Now we must speak out," they said in a statement.

"Kim and his evil regime are responsible for the death of our son Otto. Kim and his evil regime are responsible for unimaginable cruelty and inhumanity," they said.

"No excuses or lavish praise can change that."

Trump sparked a firestorm in Washington when he told reporters at the summit's conclusion that he believed Kim's claim that he didn't know what happened to Otto Warmbier during his detention.

"He knew the case very well, but he knew it later," Trump said.

Kim "tells me that he didn't know about it, and I will take him at his word."

Politicians in Washington quickly reminded the president that in 2017 he took credit for obtaining Warmbier's release. "Otto was tortured beyond belief by North Korea," Trump said at the time.

"I do not see the leader of North Korea as somebody who's a friend. We know what happened to Otto, we know what this country has done," said House Republican Leader Kevin McCarthy.

"I support the president's effort to denuclearize them, but I do not have a misbelief of who this leader is," he said, speaking of Kim.

The US government supported the Warmbier parents in their lawsuit against Pyongyang.

On December 24 a US judge ordered North Korea to pay $501 million over Warmbier's death from apparent torture.

"North Korea is liable for the torture, hostage-taking, and extrajudicial killing of Otto Warmbier," the judge said, adding that he had been used "as a pawn in that totalitarian state's global shenanigans and face-off with the United States."