"Now, the assessment of risk for Americans visiting North Korea has become too high," Young Pioneer Tours, the China-based travel agency that had taken Otto Warmbier to North Korea, said in a Facebook post.

The company, which advertised North Korea as "probably one of the safest places on Earth to visit," came under fire after Otto Warmbier was medically evacuated to the US last week, suffering from severe brain damage. He died six days later in his home town of Cincinnati, Ohio,  

"There has still been almost no information disclosed about his period in detention," the company said in its statement. "Considering these facts and this tragic outcome we will no longer be organizing tours for US citizens to North Korea."

The agency based in the Chinese city of Xian was founded in 2008 by a British expat with a motto of taking adventurous travellers to "the places your mother wants you to stay away from" including North Korea and Iran. One of a few tour agencies that visit North Korea, the firm offers trips that include scuba diving and cycling in one of the world's most impoverished countries.

The University of Virginia student was arrested at the airport as he was leaving Pyongyang in January last year and sentenced to 15 years of hard labour at a show trial for stealing a political poster from a hotel. "There had not been any previous detainment in North Korea that has ended with such tragic finality," the company said, adding that Warmbier's death had made it "reconsider" its position on accepting American tourists.

Three more US citizens are being held by North Korea. Two were teachers at a Pyongyang university funded by overseas Christian groups, and the third is a Korean-American pastor who was accused of espionage for the South.

is/ks (afp,ap)