Following the death of Otto Warmbier – the American student detained for more than a year by the North Korean government – world leaders have called on the repressive state to release all those still detained in the country, with John McCain accusing the regime of "murder".

Mr Warmbier, a 22-year-old college student, visited North Korea in January of 2016. He was detained in the country for allegedly stealing a political poster and eventually sentenced to 15 years hard labour.

He was returned home in a coma last week after 17 months. He died on Monday.

“In the final year of his life, [Mr Warmbier] lived the nightmare in which the North Korean people have been trapped for 70 years: forced labor, mass starvation, systematic cruelty, torture, and murder,” Senator McCain, a former prisoner of war, said.

“The United States of America cannot and should not tolerate the murder of its citizens by hostile powers,” the Senator added.

Mr Warmbier’s parents believe their son was tortured into a state of what doctors called “unresponsive wakefulness” before his death.

North Korean officials claim Mr Warmbier slipped into a coma after contracting botulism and taking sleeping pills. However, US doctors found no evidence of botulism upon Mr Warmbier’s release.

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Han Tae Song, North Korea's ambassador to the UN, said the country is acting “according to our national laws, and according to the international standards” in regards to detainees.

South Korean President Moon Jae-in called Warmbier’s treatment “unjust” and “cruel,” but stopped short of calling it murder.

“We cannot know for sure that North Korea killed Mr. Warmbier,” Mr Moon said in an interview with CBS. “But I believe it is quite clear that they have a heavy responsibility in the process that led to Mr. Warmbier's death.”

“I believe we must now have the perception that North Korea is an irrational regime,” said Mr Moon, who was elected in May.

“Even today, there are many Korean nationals and American citizens who are detained in North Korea,” Mr Moon added. “I also urge North Korea to return these people to their families.”

North Korea has detained two Korean-American academics and a missionary, a Canadian pastor and three South Korean nationals who were doing missionary work there. Japan says at least several dozen of its nationals are being held in the country.

The US State Department has also pushed for the release of all American citizens currently detained in North Korea.

US President Donald Trump, in a White House meeting with visiting Ukraine President Petro Poroshenko, criticised the way Mr Warmbier's case was handled in the year since his arrest, appearing to assail both North Korea and his predecessor, Barack Obama.

“What happened to Otto is a disgrace. And I spoke with his family," Mr Trump said. "His family is incredible ... but he should have been brought home a long time ago."

Experts believe the incident may have ruined hopes of improved relationships with North Korea under Mr Trump, who previously said he would be “honoured” to meet Mr Jong-un. The White House is reported to have been quietly pushing for the release of three other prisoners still detained in the country.

North Korea expert Bill Richardson told The New York Times that Warmbier’s death would “set back any serious discussion about a diplomatic dialogue”.

“I think the first objective has to be to get the three other Americans out, and get a full explanation of what happened to Otto Warmbier,” he said.

White House spokesman Sean Spicer said a meeting between Mr Trump and Mr Kim was less likely following Mr Warmbier's death.

Mr Spicer said Mr Trump would be willing to meet Mr Kim under the right conditions, but that, “clearly we're moving further away, not closer to those conditions.”

US relations with China, one of North Korea’s biggest allies, could also be affected by the death of the American student. The US has already placed extensive sanctions on the North Korean regime, but has yet to apply "secondary sanctions" on Chinese companies that do business with the country.

Mr Warmbier's death appeared likely to increase pressure on Beijing ahead of a US-China Diplomatic and Security Dialogue on Wednesday.

The talks will pair U.S. Secretary of State Rex Tillerson and Defence Secretary James Mattis with China's top diplomat, State Councilor Yang Jiechi, and General Fang Fenghui, chief of state of the People's Liberation Army.

The State Department says the dialogue will focus on ways to increase pressure on North Korea to give up its nuclear and missile programmes, but also cover such areas as counter-terrorism and territorial rivalries in the strategic South China Sea.

Mr Trump, however, seemed to signal he would not increase pressure on China in a tweet.

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

In a further sign that US-Chinese relations will remain stable, a White House aide said Mr Trump's daughter Ivanka Trump and her husband, White House senior adviser Jared Kushner, were invited by the Beijing government to visit China later this year.

Mr Spicer said the Trump administration would "continue to work with [China] and others to put the appropriate pressure on North Korea".

Mr Warmbier’s family, meanwhile, says they are choosing to focus on the short time they had with their son, ahead of his funeral on Thursday.