The news comes as the North Korean army on Friday vowed a "merciless" response to any US provocation, according to the country's official news agency KCNA.

Reports of activity at a nuclear test site in North Korea ahead of Saturday's 105th anniversary of the birth of the country's founder Kim Il-Sung have fuelled speculation it could imminently carry out a sixth test.

The last Air China flight between the two capitals arrived in Beijing at 6 pm Friday, CCTV said, without elaborating on the suspension.

It noted however that the thrice-weekly route, first established in 2008, was often cancelled because of lack of passengers, as well as being subject to "seasonal adjustments" such as cancellations or reductions in frequency during the low-demand winter.

North Korea's flag-carrier Air Koryo remains the only company that continues to operate flights into the country.