“North Korea’s economy continues to operate despite being increasingly isolated by the tightening international sanctions campaign,” said Ben Davis, a former U.S. Treasury official who heads research at Kharon, a technology firm that identifies sanctions-related risks for companies.

In recent months, both the United Nations Security Council and the U.S. have ramped up penalties against North Korea, including new bans on joint ventures to deter Mr. Kim’s nuclear weapons program. But the rules have proved to be porous.

U.N. and U.S. officials have yet to declare any company to be in violation of the joint-venture-ban. But officials are particularly alarmed over the links that exist between North Korea and companies from China, Malaysia, Singapore, Hong Kong and other countries that maintain commercial ties with the pariah nation.

Some of the ventures appear to be enormously lucrative to North Korea. For example, U.S. government reports show that North Korea commands a significant portion of an illicit international cigarette trade worth billions of dollars per year.

U.S. officials and a high-level North Korean defector with direct knowledge of Mr. Kim’s financing operations say most profits go directly into Pyongyang’s coffers. That cash, these people say, is used to fund the military, the country’s nuclear weapons programs and the luxury goods provided to the political and military elite who help to keep Mr. Kim in power.

The U.S. Treasury says that it doesn’t comment on investigations, including to confirm whether or not one exists. But officials have said the Treasury aggressively targets North Korea’s efforts to evade sanctions.

The U.N. press office referred questions to the U.N. Security Council presidency, which referred queries to the U.N. sanctions committee for North Korea, which didn’t respond to requests for comment.

One major company still involved in North Korean joint ventures is Egypt’s Orascom Telecom Media and Technology. 

In its financial statements for the six-month period ending in June, the company reported a 75% ownership stake in a mobile phone joint venture with North Korea’s Postal and Telecommunications Co. It also lists a stake in a North Korean lender called Orabank which it had previously said it had liquidated. Orascom recorded net assets from the mobile phone venture to be worth $1.2 billion, and said it received dividends from it worth $15 million in 2016 and around $39 million in the first two months of 2017. No more recent information was available.

It’s unclear if Orascom is violating any sanctions regime. The U.N. ban allow companies to seek waivers from the international body and provides an exception for “non-commercial public utility infrastructure projects not generating profit.”

Orascom Chairman Naguib Sawiris, who has U.S. citizenship, recently told The Wall Street Journal that the company is compliant with all U.N. resolutions and has no plans to leave North Korea.

 The Egyptian company has said it “has a ring-fencing process for its Korean subsidiary…to make sure it is abiding with all applicable laws,” and it had submitted applications to the U.S. Treasury’s Office of Foreign Assets Control and U.N. Security Council, via Egyptian authorities, for licenses to continue its business in North Korea.

An Orascom spokeswoman said the firm provides “an important service” to North Koreans. “We believe allowing [a] population to communicate is a good thing,” Mr. Sawiris said.

Egypt’s Embassy in Washington declined to comment about Orascom.

North Korea’s global links underscore the difficulty the U.N. faces as the organization tries to get member countries to enforce compliance with the sanctions meant to sever the Kim regime’s ties to the world. Scores of member countries haven’t filed the required implementation reports. U.N. investigators complain many countries respond inadequately to allegations and evidence of sanction violations. Many member states either have weak domestic law enforcement agencies or competing political or legal priorities, leaving sanction violators unchecked, analysts say.

Pyongyang’s global corporate ties also represent a potential liability to financial institutions looking to avoid penalties for activities linked to the regime. Kharon warns that other North Korea joint ventures may be hard to spot, a risk for financial institutions and investors.

“Identifying undisclosed North Korea interests is a mounting challenge for commercial institutions,” Mr. Davis said.

Another company, Charoong Thai Wire and Cable Public Company Ltd. of Thailand, maintains connections to North Korea through two joint ventures with North Korea’s Postal and Telecommunications Company to operate the country’s internet, telephone and cable TV services.

Charoong, in its 2016 annual report, said it had a 25% ownership in a Thai company venture with Pyongyang in the North East Asia Telephone & Telecommunications Co. And it reported a 20% ownership in a Hong Kong company that is a partner in the North Korean firm, Star Joint Venture, that runs the country’s internet service. Charoong said the two units provided it nearly $4 million of revenue last year.

The company didn’t respond to requests for comment. Thailand hasn’t filed a filed a report on its sanctions compliance to the U.N. since 2009. But a spokesman at the Thai Embassy in Washington said the country “is committed to fully implementing the United Nations Security Council resolutions relating to North Korea.” He declined to comment further.

Meanwhile, British American Tobacco, which owns Lucky Strike cigarettes and other brands, sold its stake in a North Korean venture with the government last year amid tightening sanctions and a probe into counterfeits, said a person familiar with the matter.

But the current registered owner of the venture is Singapore-based Lucky Greenbird, which is owned by another Singapore-registered firm incorporated last year, which is listed through yet one other. All list the same director, secretary and registered addresses each other. Raymond Ng Say Than, a former BAT executive, is listed in those corporate records as a director. He didn’t respond to requests for comment.

Singapore, which late last year said it was suspending all trade with North Korea, is implementing U.N. security council sanctions “fully and faithfully,” said Nurasyikin Azman, the first secretary of information at the country’s embassy in Washington. He didn’t respond to requests for comment about the specific companies.