United Nations sanctions monitors are investigating dozens of suspected cyberattacks by North Korea that raked in $3 billion to help it further develop its nuclear weapons program, according to excerpts of an unpublished U.N. report reviewed by Reuters.

"The Democratic People's Republic of Korea (DPRK) continued to flout Security Council sanctions," a panel of independent sanctions monitors reported to a Security Council committee, using North Korea's formal name.

"It further developed nuclear weapons and produced nuclear fissile materials, although its last known nuclear test took place in 2017," wrote the monitors, who also said Pyongyang had continued ballistic missile launches, put a satellite into orbit and added a "tactical nuclear attack submarine" to its arsenal.