North Korea's intricate overseas financial network is creaking under the strains of Washington's economic screws on the impoverished nuclear armed regime, a research report said.

The United Nations, United States, European Union and several individual countries have slapped multiple sets of economic sanctions on the North for its menacing nuclear and ballistic missile programmes, forcing Pyongyang to come up with illicit ways to evade them.

The North operated a complex offshore financial network to maintain the flow of hard currency, said a report by Washington-based security research group C4ADS and the Sejong Institute in Seoul.

But doing so meant Pyongyang had lost control of its assets, it added.