The American-led effort to isolate North Korea from all aspects of the international community has apparently spread to New Zealand, with a group of North Korean academics - including a historian, a philosopher and a linguist - denied visas for a conference this week.

The 10-member delegation from the Pyongyang-based Academy of Social Sciences was not permitted to attend the International Society for Korean Studies conference in Auckland.

Their specialties include Korean folklore, philosophy, classical literature, history and education. There were to be accompanied by two "minders", as is standard for North Korean groups travelling abroad.

One of the academics due to travel was Jo Hui Sung, who is renowned in his field: the history of the Koguryo era, one of the three kingdoms on the Korean Peninsula until the seventh century.

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But the New Zealand government rejected the visa applications last Friday to comply with sanctions against North Korea, according to people familiar with the process.

"They said it was because of the United Nations sanctions," said one, who spoke on the condition of anonymity to give details of the decision.

As Kim Jong Un's regime has continued to defy the international community by launching missiles, the United Nations has imposed sanctions to try to cut off North Korea's ability to buy parts for its weapons programme by clamping down on both logistics and financing.

At the same time, the United States has imposed much more aggressive unilateral sanctions against North Korea, blacklisting individual people and companies that the US Treasury Department claims are involved in running or financing the weapons programme.

However, none of the sanctions, whether unilateral or multilateral, target humanities professors.

The New Zealand foreign ministry declined to comment, referring inquiries to the immigration department.

"Immigration New Zealand can confirm that these visa applications were declined for not meeting immigration instructions," said Marc Piercey, a spokesman for Immigration New Zealand, declining to comment further for "legal and privacy reasons".

The visa decision was made just days after Recorded Future, a threat intelligence firm, released a report saying that North Koreans were accessing the internet through a handful of countries, including New Zealand. However, it was not clear whether the report had anything to do with the decision.

The International Society for Korean Studies' two-day conference was held at the University of Auckland and was attended by 130 academics from around the world, including the United States, Europe, China and South Korea.

The Japan-based group convenes the conference every second year, with the last event being held in Austria in 2015. Twelve North Koreans, many of them the ones slated to travel to New Zealand this week, attended.

Proponents of engagement were dismayed by the news.

"If you're interested in bringing about gradual change in North Korea, surely one of the best ways to do so is by bringing out as many people as possible and exposing them to the outside world," said Stephen Epstein, who teaches Korean studies at Victoria University of Wellington, who has been involved in bringing previous groups of North Koreans to New Zealand.

New Zealand has hosted other delegations of North Koreans, including three English professors who travelled to a New Zealand university last year, and two North Koreans who attended a study group of the Council for Security Cooperation in the Asia Pacific in Auckland in March.

But the New Zealand government has also denied visa applications from North Koreans in the past.

As North Korea advances its missile programme and touts its ability to strike the United States mainland, Washington has been leading an international campaign to isolate Pyongyang.

It is putting pressure on foreign governments that allow North Korean workers into their countries - labour exports have become a major source of hard currency for the regime - to stop the practice. It has also been urging other governments to cut off diplomatic relations with North Korea.