North Korea has called itself the “biggest victim” over the death of an American student who was detained for more than a year and died days after being released in a coma.

Pyongyang's official Korean Central News Agency (KCNA) denied that North Korea cruelly treated or tortured Otto Warmbier and accused the United States and South Korea of a smear campaign that insulted what it called its “humanitarian” treatment of him.

The comments published by the agency were North Korea's first reaction to Mr Warmbier's death in a US hospital on Monday after it released him for what it called humanitarian reasons.

Doctors at the hospital said Mr Warmbier had suffered a severe neurological injury from an unknown cause.

Relatives say they were told the 22-year-old University of Virginia student had been in a coma since shortly after he was sentenced to 15 years of hard labour in North Korea in March 2016.

His family and others have blamed North Korea for his condition.

Mr Warmbier was accused of stealing a propaganda poster.

Through statements on KCNA, North Korea said it dealt with him according to its domestic laws and international standards.

“Although we had no reason at all to show mercy to such a criminal of the enemy state, we provided him with medical treatments and care with all sincerity on a humanitarian basis until his return to the US ... considering that his health got worse,” the agency quoted a spokesman of Pyongyang's foreign ministry as saying.

The spokesman also said that “groundless” speculation of torture and beatings could be refuted by American doctors who came to the North to examine Mr Warmbier before his release and allegedly acknowledged that North Korean doctors had “brought him back alive” after his heart nearly stopped.

While Pyongyang accepted US demands for Mr Warmbier's return on humanitarian grounds, Washington “totally distorted this truth and dared to clamour about 'retaliation' and 'pressure”' on “dignified” North Korea, the spokesman told KCNA.

“To make it clear, we are the biggest victim of this incident and there would be no more foolish judgment than to think we do not know how to calculate gains and losses,” the spokesman said.

“The smear campaign against DPRK staged in the US compels us to make firm determination that humanitarianism and benevolence for the enemy are a taboo and we should further sharpen the blade of law,” the spokesman added, referring to North Korea by its formal name, the Democratic People's Republic of Korea.

The spokesman said it was a “mystery” as to why Mr Warmbier died days after returning home, but compared his death to the case of another American detainee, Evan Hunziker.

Mr Hunziker was detained in North Korea for months in 1996 for illegally crossing the border and committed suicide less than a month after he returned to the United States later that year.

The spokesman did not describe how Mr Hunziker died, but claimed that the United States then “totally ignored” his death.

A separate KCNA article published hours earlier also criticised South Korea for using Mr Warmbier's case to seek the release of other detainees, including six South Korean citizens.

South Korean President Moon Jae-in said in an interview with CBS television earlier this week that it was clear North Korea bears a heavy responsibility for Mr Warmbier's death.

The article said South Korea was tarnishing North Korea's image with “slanderous talk about cruel treatment and torture”.

It demanded that South Korea return 12 restaurant workers who defected to the South last year.

In pictures: North Korea military drill Show all 8 1 /8 In pictures: North Korea military drill In pictures: North Korea military drill North Korea's leader Kim Jong Un watches a military drill marking the 85th anniversary of the establishment of the Korean People's Army (KPA) KCNA/Handout via REUTERS In pictures: North Korea military drill A military drill marking the 85th anniversary of the establishment of the Korean People's Army (KPA) is seen in this handout photo by North Korea's Korean Central News Agency (KCNA) KCNA/Handout via REUTERS In pictures: North Korea military drill A military drill marking the 85th anniversary of the establishment of the Korean People's Army (KPA) is seen in this handout photo by North Korea's Korean Central News Agency (KCNA) KCNA/Handout via REUTERS In pictures: North Korea military drill A military drill marking the 85th anniversary of the establishment of the Korean People's Army (KPA) KCNA/Handout via REUTERS In pictures: North Korea military drill A military drill marking the 85th anniversary of the establishment of the Korean People's Army (KPA) KCNA/Handout via REUTERS In pictures: North Korea military drill This image made from video of still images broadcast in a news bulletin by North Korea's KRT, shows what was said to be a 'Combined Fire Demonstration' held to celebrate the 85th anniversary of the North Korean army, in Wonsan, North Korea. KRT via AP Video In pictures: North Korea military drill This image made from video of still images broadcast in a news bulletin by North Korea's KRT, shows what was said to be a 'Combined Fire Demonstration' held to celebrate the 85th anniversary of the North Korean army, in Wonsan, North Korea. KRT via AP Video In pictures: North Korea military drill This image made from video of still images broadcast in a news bulletin by North Korea's KRT, shows what was said to be a 'Combined Fire Demonstration' held to celebrate the 85th anniversary of the North Korean army, in Wonsan, North Korea. KRT via AP Video

South Korea said the women defected on their own, while North Korea claimed they were deceived and abducted to the South.

The United States, South Korea and others often accuse North Korea of using foreign detainees to wrest diplomatic concessions.

Three Americans remain in custody in the North.