The United States demands liberation of three Americans held in North Korea

This undated picture released from North Korea's official Korean Central News Agency (KCNA) on June 20, 2017 shows North Korean leader Kim Jong-Un (C) visiting a newly-built dental sanitary goods factory at an undisclosed location in North Korea. (AFP PHOTO/KCNA VIA KNS)

The United States has called on North Korea to release “as soon as possible,” three Americans who are still detained by Pyongyang, following the death of the college student, Otto Warmbier.

"We hold North Korea accountable for Otto Warmbier's unjust imprisonment," US State Department spokeswoman Heather Nauert said at a news briefing on Tuesday. "We want to see three other Americans who were unjustly detained brought home as soon as possible.”

Two of the detainees were teachers at a Pyongyang university funded by overseas Christian groups, and the third was a Korean-American pastor accused of espionage for the South.

Otto Frederick Warmbier, a University of Virginia student, attends a news conference in Pyongyang, North Korea, on February 29, 2016. (Photo by Reuters)

Warmbier was released on June 13 in a state of coma after Joseph Yun, the State Department’s special envoy on North Korea, paid a visit to Pyongyang and demanded his release.

North Korean media, however, said the 22-year-old student’s release had been based on a court decision and “on humanitarian grounds.”

While suffering from severe brain damage, Warmbier, died at a Cincinnati Medical Center on Monday. The American college student had spent 17 months in detention, acknowledging that he had tried to steal a banner containing a political slogan from the hotel where he had been staying.

'A disgrace for US'

US President Donald Trump has, meanwhile, called Warmbier’s death a "total disgrace," adding that the college student might have been alive if he had been brought home sooner.

“It’s a disgrace what happened to Otto. It’s a total disgrace what happened to Otto,” Trump said during an event in the Oval Office. “It should never, ever be allowed to happen, and, frankly, if he were brought home sooner, I think the result would have been a lot different... He should have been brought home that same day. The result would have been a lot different.”

Trump also issued a statement offering his “deepest condolences” to the Warmbier family and further denounced “the brutality of the North Korean regime.”

Warmbier’s death unfortunate: China

China, North Korea’s main ally, expressed sorrow over the death of the US student and called on Washington and Pyongyang to resolve tensions through dialogue.

“I think this is an unfortunate thing,” Chinese Foreign Ministry spokesman Geng Shuang said at a regular news briefing. “We hope that North Korea and the US can handle it appropriately.”

Geng Shuang, China's Foreign Ministry spokesman

Trump also thanked China for trying to resolve tensions with North Korea but declared that Beijing's "efforts" had failed.

"While I greatly appreciate the efforts of President Xi & China to help with North Korea, it has not worked out. At least I know China tried!" the US president said.

North Korea accuses the US of plotting with regional allies to topple its government.

Over the past weeks, Washington and Pyongyang have traded a barrage of military threats. The US says it is concerned by North Korea’s nuclear and missile tests.

Pyongyang has defied sanctions and international pressure, saying it will continue to strengthen its military capability to protect itself from the threat posed by the presence of US forces in the region.