U.S. Secretary of Homeland Security Alejandro Mayorkas says North Korea largely funded its weapons of mass destruction programs over the last two years through cyber heists of cryptocurrencies and hard currencies worth more than one billion U.S. dollars.

The Voice of America reported that Mayorkas made the remarks in a speech at the Singapore International Cyber Week on Tuesday. 

The secretary said the North has engaged in such cyber heists “with near impunity.”

He said hostile nations like North Korea, Russia, Iran and China, and cybercriminals around the world, “continue to get more sophisticated and create more adverse consequences,” adding that such cyber operations threaten economic and national security.

He cited an FBI report that estimated that the U.S. saw more than 25-hundred ransomware attacks last year alone. 

Mayorkas said Washington is "building strong operational relationships" to tackle ransomware attacks through its ransomware working groups with South Korea and the European Union.