The missiles were fired just a  day after South Korea and the United States staged joint air drills, involving B-1B bombers, media reports said.

The Joint Chiefs of Staff (JCS) of South Korea said it detected the launch from the Sukchon area in South Pyongan Province between 7 a.m. and 7:11 a.m., and that the missiles flew some 390 kilometers and 340 km, respectively, reports Yonhap news agency.

Hours after the launch, the North's official Korean Central News Agency (KCNA) reported that the artillery unit of the Korean People's Army fired two shots from the 600-mm multiple rocket launcher during firing drills, and that they flew 395 km and 337 km, respectively.

The weapon system is a "tactical nuclear attack means boasting of the great might powerful enough to assign only one multiple rocket launcher with four shells so as to destroy an enemy operational airfield," the KCNA said in an English-language report as quoted by Yonhap.