A North Korean flag flies on a mast at the Permanent Mission of North Korea in Geneva, October 2, 2014. (Photo: REUTERS/Denis Balibouse)

The country tested another kind of a nuclear-capable unmanned underwater attack weapon called "Haeil-2", over a week after it disclosed a new underwater drone system dubbed "Haeil-1", which translates to tsunami in Korean, designed to make sneak attacks in enemy waters. 

During the underwater strategic weapon system test from Tuesday to Thursday state media KCNA said that the drone cruised 1,000 km of underwater distance for more than 71 hours and successfully hit a simulated target. 

North Korea has ramped up its military activities in recent weeks, protesting that the United States and South Korea conduct joint military exercises. 

It unveiled new, smaller nuclear warheads and fired an intercontinental ballistic missile capable of striking anywhere in the United States.