A day after US student Otto Warmbier was laid to rest at a funeral service in his home town of Cincinnati on Thursday, the North Korean foreign ministry released a statement to local state-controlled television saying his death was a mystery and dismissing accusations that he had died because he was tortured and beaten during his captivity, according to Reuters.

Instead, the North’s foreign ministry blamed the Obama administration for Warmbier's death, which never formally requested Warmbier’s release, claiming Warmbier was “a victim of the policy of strategic patience.”

"The fact that Warmbier died suddenly in less than a week just after his return to the U.S. in his normal state of health indicators is a mystery to us as well," the foreign ministry was quoted by KCNA as saying.

Warmbier, 22, was arrested in the reclusive country while visiting as a tourist. He was sentenced to 15 years of hard labor for trying to steal an item bearing a propaganda slogan from his hotel, North Korea state media said. He was brought back to the United States last week with brain damage, in what doctors described as state of "unresponsive wakefulness", and died on Monday. US doctors who had traveled to the North last week to evacuate him had recognized that the former student had been provided with medical treatment, according to a ministry official.

"Although Warmbier was a criminal who committed a hostile act against the DPRK, we accepted the repeated requests of the present US administration and, in consideration of his bad health, sent him back home on humanitarian grounds," the spokesman said.

The exact cause of Warmbier's death remains unclear. Officials at the University of Cincinnati Medical Center, where he was treated after his return from the North, declined to provide details, and his family asked the Hamilton County Coroner on Tuesday not to perform an autopsy.

In a written statement, the foreign ministry claimed the US was spreading lies about North Korea’s role in Warmbier’s death.

“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 US should ponder over the consequences to be entailed from its reckless and rash act.”