Cindy Warmbier, mother of late US prisoner in North Korea Otto Warmbier, speaks at a seminar on North Korean abductees in Washington, DC, on May 3, 2019. AFP-Yonhap

The mother of Otto Warmbier, an American college student who died in 2017 after being detained in North Korea, made a plea Friday for continued pressure on the regime.

Cindy Warmbier spoke at a seminar alongside family members of South Korean, Japanese and U.S. citizens who are believed to have been abducted by North Korea in past decades.

"Unless we keep the pressure on North Korea, they are not going to change," she said at the event co-hosted by the Hudson Institute, the Committee for Human Rights in North Korea, and the Japanese government.

"I am very afraid that we're going to let up on this pressure. So I need everyone here to keep the pressure on everybody you can. There are still a lot of families here that deserve to see their family members," she said.

Cindy Warmbier, mother of late US prisoner in North Korea Otto Warmbier, speaks at a seminar on North Korean abductees in Washington, DC, on May 3, 2019. AFP-Yonhap

The Warmbier case has received renewed attention since The Washington Post reported last week that the North Koreans had demanded US$2 million from the U.S. government to cover his hospital fees.

The University of Virginia student fell into a coma shortly after he was detained in Pyongyang in early 2016 for allegedly trying to take down a political poster.

He spent the next year and a half hospitalized there before he was released and returned to the U.S. in June 2017, only to die several days later.

"North Korea to me is a cancer on the earth," Cindy Warmbier said. "And if we ignore this cancer, it's not going to go away. It's going to kill all of us. We don't even know we have this cancer, so that's why I talk. There is a cancer, I can tell you."

U.S. President Donald Trump has denied that any money was paid to North Korea for Warmbier's release.

Otto Frederick Warmbier, center, a University of Virginia student who was detained in North Korea since early January, is taken to North Korea's top court in Pyongyang, North Korea, in this photo released by Kyodo March 16, 2016. Reuters-Yonhap

In February, he told a press conference following his second summit with Kim Jong-un in Vietnam that he confronted the North Korean leader about Warmbier's death.

"He tells me he didn't know about it, and I take him at his word," Trump said at the time.

Cindy Warmbier thanked the U.S. government for getting her son out of the North, but she also questioned the administration's diplomatic efforts to dismantle the regime's nuclear weapons program.

"This is not only a nuclear problem. This is a problem that we're dealing with absolute evil," she said. "There's a charade going on right now. It's called diplomacy. How can you have diplomacy with someone who never tells the truth? That's what I want to know. I'm all for it, but I'm very skeptical. He lies, he lies, he lies, all for himself."

Citing the North's notorious concentration camps, she added: "The only difference between Hitler and him is he's doing it to all of his people and to other people, too." (Yonhap)