The Japanese Joint Staff announced on Thursday that Japan and the US have conducted joint air force drills following the recent missile launch by the Democratic People's Republic of Korea (DPRK).

In a statement, the Joint Staff noted that the "Japan Self-Defense Forces and US Armed Forces conducted a bilateral exercise on Thursday, April 13 amid an increasingly severe security environment surrounding Japan, including North Korea's suspected high angle ICBM-class Ballistic Missile launch."

According to the statement, the drills entailed four Japanese F-2 fighters and an equal number of US F-16 jets.

Earlier on April 8, the Democratic People's Republic of Korea's (DPRK) national news agency, KCNA, revealed that two weeks after having tested the Haeil-1 underwater nuclear drone, the DPRK's Academy of Defense Science conducted a second test for Haeil-2.

According to the agency, "The underwater nuclear attack drone 'Haeil-2'," which "cruised 1,000 kilometers of simulated underwater distance," is capable of unleashing a "radioactive tsunami".

KCNA stated that the academy tested the "underwater strategic weapon system from April 4 to 7," adding that "the test warhead accurately detonated underwater. The test perfectly proved the reliability of the underwater strategic weapon system and its fatal attack ability."

Additionally, the agency reported that "this nuclear underwater attack drone can be deployed at any coast and port or towed by a surface ship for operation" and that its mission is to "stealthily infiltrate into operational waters and make a super-scale radioactive tsunami...to destroy naval striker groups and major operational ports of the enemy."

DPRK leader Kim Jong Un, who supervised both tests personally, urged to increase the country's nuclear force capabilities and become ready to respond to any potential "attack" by the enemy. 

Read more: US-South Korea drills driving tensions to 'brink of nuclear war': DPRK