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The United Nations is investigating two North Korean missile and arms companies suspected of operating in Iran in possible violation of internationalsanctions, according to a report by a U.N. panel of experts.

The presidents of top North Korean regime arms firms, KOMID, which exports equipment for ballistic missiles and other weapons, and Green Pine, which sells conventional arms, recently traveled to Iran, according to air passenger documents cited by the report by the U.N. panel.

A U.N. member state informed the panel that the two North Korean arms firms — which are both blacklisted by the United Nations — are “extremely active in Iran now,” Hugh Griffiths, coordinator of the U.N. panel assessing sanctions on North Korea, told NBC News in an exclusive television interview.

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“There's an active investigation into who exactly is at the North Korean embassy in Tehran and what they're doing there,” Griffiths said.

The U.N. panel previously documented how KOMID was operating in Iran until 2016 with the help of North Korean diplomats, whom Iran eventually expelled. Two North Korean representatives, Kim Yong Chol and Jang Jung Son, were monitored flying between Tehran and Dubai more than 262 times between 2014 and 2016, suspected of carrying cash to evade sanctions on North Korea, according to the previous U.N. account.

The United Nations is now looking into allegations that North Koreans working for the blacklisted arms companies are back in Tehran and engaged in cash couriering for suspected illicit activities, according to the U.N. report, which was reviewed by NBC News.

The U.N. panel wrote to Iran requesting copies of passports of all North Korean diplomats in Iran but so far, Tehran has not supplied the requested information, according to the report.

The U.N. panel obtained passport information on multiple North Korean diplomats blacklisted previously as representatives of KOMID or Green Pine, and have supplied the information to Iranian authorities, according to the report.

The passport details include the two North Korean representatives, Kim Yong Chol and Jang Jung Son, identified during 2014-2016 as allegedly carrying cash on flights between Tehran and Dubai.

North Korea has long been accused of pursuing illicit arms sales around the world, from ballistic missiles to submarines to automatic rifles, in order to earn hard currency and enlist assistance from other governments. Pyongyang has sold arms to Iran since the Iran-Iraq war in the 1980s, including various ballistic missiles and technology.

Two North Korean representatives, Kim Yong Chol (above) and Jang Jung Son, were monitored flying between Tehran and Dubai more than 262 times between 2014 and 2016, suspected of carrying cash to evade sanctions on North Korea, according to the previous U.N. account.

The U.N. panel of experts' latest report found North Korea is successfully evading United Nations sanctions through increasingly sophisticated methods, enabling the regime to import more oil, expand coal exports, sell weapons and hack into foreign banks.

The sanctions are designed to prevent Pyongyang from funding its nuclear weapons and ballistic missile programs, but North Korea has carved out new ways to flout the U.N. sanctions, including deceiving global banks, insurers and commodity traders, Griffiths said.