Kato came across evidence of the two nations' role in facilitating North Korea's illegal activities in documents submitted to the Hong Kong Companies Registry in the name of New East International Trading Limited.

Tokyo had previously identified the firm as being involved in the Stalinist state's illegal arms trade.

In August 2004, New East International was listed in the documents as being registered at the China Overseas Building on Hennessy Road in Wan Chai.

The firm's two directors were named as Chol Han and Ju Ok-hui. Both men were identified as residents of Sokam 18, Botonggang District, Pyongyang, and holding North Korean passports.

But by 2006, the annually updated papers listed their home addresses as Room C0702, Soho New Town, No88 Jianguo Road, Beijing.

Both men currently hold passports with consecutive numbers issued by Kiribati.

In 2006, the United Nations imposed trade and military sanctions on Pyongyang for testing a nuclear weapon.

By 2008, the two men had moved their Hong Kong offices to Unit 1021 of the Ocean Centre in Tsim Sha Tsui, and were listed as having Seychelles passports.

"My guess is that these are not the only North Korean operatives who have done this and are travelling on other passports even today," Kato said.

"One of my concerns is that it is clear these men have been able to change their nationalities several times," he said. "If, for example, they can use those to get a Philippines passport, then it would be relatively easy for them to then get a US passport."

Tokyo placed New East International on a watch list after three employees of its Japanese branch were arrested in 2009 and convicted of shipping banned technology. They exported or tried to export components that can be used to produce gyroscope systems to guide missiles.

North Korea is still subject to UN sanctions that were tightened recently in the wake of its failed missile launch in April.

The North Koreans linked to the Hong Kong branch of New East International apparently took advantage of "investor passports", first issued by Kiribati in 1996 for individuals who would invest in the country.

Under world pressure, the scheme was halted in 2004, although the documents for Chol and Ju were issued on November 2, 2005.

The Seychelles introduced a similar scheme - which the United States condemned - for anyone willing to invest US$10 million in the country. The scheme was supposedly cancelled in July 2000, but the Seychelles issued passports to Chol and Ju on March 26, 2007.

New East International's Hong Kong office was deregistered in 2009, but Kato believes Chol and Ju have likely started anew in another city.

"North Korea is one of the worst nuclear proliferators in the world and they have been selling weapons of mass destruction to rogue states and terrorist groups, such as Iran, Syria and Hezbollah," Kato said.

"Kiribati and Seychelles must revoke all passports issued to North Koreans - not only these two - and hand over information to the UN Security Council and the countries concerned."

Dozens of small private firms in Hong Kong are known to have had business dealings with North Korean partners in recent years and North Korean-linked ships have long been occasional visitors to the city.

In Tokyo, the consulates of Kiribati and the Seychelles would not comment on the allegations.

"Presumably, North Korea is saying that it wants to improve its scientific and technological capabilities, and I think we have seen that they are willing to do everything they can to achieve that," said Hiroyasu Akutsu, an expert on North Korea.