Koryo Tours said the ban would be announced on July 27 and would go into effect 30 days later. It did not say how long the ban would last.
Another tour operator, Young Pioneer Tours, said in a Twitter message that it had also been informed of the ban, citing the same date.
Young Pionner was the agency that took US student Otto Warmbier to North Korea. He was subsequently arrested there and sentenced to 15 years of hard labour.
(Reporting by Se Young Lee and James Pearson; Editing by Robert Birsel)