US student Otto Warmbier has died in a Cincinnati hospital only days after being released in a coma from 17 months of detention in North Korea, his family said in a statement last night.

Mr Warmbier, 22, who was arrested in North Korea while visiting as a tourist, had been described by doctors who examined him last week as having suffered extensive brain damage that left him in a state of "unresponsive wakefulness".

Physicians said last Thursday that Mr Warmbier had shown no sign of understanding language or of awareness of his surroundings, and had made no "purposeful movements or behaviours."

The circumstances of his detention in North Korea, and what medical treatment he received there, remained a mystery.

However relatives have said his condition suggests he was physically abused by his captors.

"Unfortunately, the awful torturous mistreatment our son received at the hands of the North Koreans ensured that no other outcome was possible beyond the sad one we experienced today," the family said in a statement following his death at 2.20pm (7.20pm Irish time).

His family said that Mr Warmbier had lapsed into a coma in March 2016, shortly after he was sentenced to 15 years of hard labour in North Korea.

He was arrested, according to North Korean media, for trying to steal an item bearing a propaganda slogan.

North Korea released Mr Warmbier last week, saying he was being freed "on humanitarian grounds."

The North Korean mission to the United Nations was not immediately available for comment.

The University of Virginia student's father, Fred Warmbier, said last week that his son had been "brutalised and terrorised by the North Korean government and that the family disbelieved North Korea's story that his son had fallen into a coma after contracting botulism and being given a sleeping pill.

Doctors who examined Mr Warmbier after his release said there was no sign of botulism in his system.

Mr Warmbier was freed after the US State Department's special envoy on North Korea, Joseph Yun, traveled to Pyongyang and demanded the student's release on humanitarian grounds, capping a flurry of secret diplomatic contacts, a US official said last week.

Tensions between the two nations have been heightened by dozens of North Korean missile launches and two nuclear bomb tests since the beginning of last year.

North Korea has also vowed to develop a nuclear-tipped intercontinental ballistic missile capable of hitting the US mainland.

US President Donald Trump offered condolences to the Warmbier family and denounced North Korea as a brutal regime with no respect for "basic human decency" and said Mr Warmbier faced tough conditions.

Susan Thornton, the US acting assistant secretary of state for east Asia, said earlier that the United States was concerned for the welfare of the three other US citizens still held in North Korea - Korean-Americans Tony Kim, Kim Dong Chul and Kim Hak Song.

Young Pioneer Tours, the group with which Mr Warmbier traveled to North Korea, will no longer be organising tours for US citizens to the isolated country, a company director said in a statement.