The North Korean government has denied mistreating US student Otto Warmbier, who fell into a coma while being held in prison in the communist state.

Mr Warmbier died without recovering on Monday, having been brought back to the US last week. His family blames the North Korean authorities for his death.

US President Donald Trump called the North a “brutal regime”.

A spokesman in Pyongyang was quoted by Reuters as saying Mr Warmbier’s death was “a mystery”.

Mr Warmbier, 22, a student at the University of Virginia, had been travelling with a tour group when he was arrested at Pyongyang airport in January 2016.

Accused of stealing a propaganda sign from a hotel, he was sentenced to 15 years of hard labour.

His family had no news of him until 13 June when Pyongyang announced he had been in a coma since his trial, attributing it to botulism.

More than 2,500 family, friends and well-wishers gathered for his funeral in Ohio on Thursday.

• Will we ever know what happened to Otto Warmbier?
• How did Otto Warmbier’s holiday end in his death?
• Is visiting North Korea too risky?
• How harsh is prison in North Korea?

What does the North say to accusations it caused Mr Warmbier’s death?

The North Korean spokesman quoted by Reuters suggested the student had returned to the US “in his normal state of health”.

“The fact that Warmbier died suddenly in less than a week just after his return to the US in his normal state of health indicators is a mystery to us as well,” he said.

Accusations that the student died because of torture and beating during his captivity were “groundless”, he added.

A North Korean spokesman quoted by AFP news agency accused the US of mounting a “smear campaign”.

“Our relevant agencies treat all criminals… thoroughly in accordance with domestic laws and international standards and Warmbier was not an exception,” a spokesman for the National Reconciliation Council said.

“Those who have absolutely no idea about how well we treated Warmbier under humanitarian conditions dare to utter ‘mistreatment’ and ‘torture’.”

What do US doctors say?

They say he suffered a “severe neurological injury”, the most likely cause of which was a cardiopulmonary arrest that had cut the blood supply to the brain.

They say there was no evidence he suffered from botulism.

A post-mortem examination was not carried out at the request of the family.

The family maintain he died as a result of “awful torturous mistreatment”.

How may relations between the US and North Korea be affected?

Mr Warmbier’s death heightened tensions between the two countries, already at loggerheads over the North’s nuclear and missile programmes.

Pyongyang has called Mr Trump a “psychopath”.

President Trump has said he is determined to “prevent such tragedies from befalling innocent people at the hands of regimes that do not respect the rule of law or basic human decency”.

North Korea was already high on President Trump’s agenda, the BBC’s Steve Evans reports from Seoul.

This death and the public condemnation by the Warmbier family on television keeps the regime’s behaviour squarely in front of the American public, our correspondent adds.

Meanwhile, North Korea is holding three other Americans as well as six South Koreans.