North Korea has threatened the use of "strategic means" after a joint military exercise between the South Korean military and the United States featuring the use of a US strategic bomber, which Pyongyang called a strategic threat, Yonhap reported.

"[North Korea] will counter the strategic threat of the US and other enemies with strategic means and continue its responsible military activities to control and manage the unstable security environment on the Korean Peninsula with powerful deterrence," a North Korean official said, adding that their move to increase their nuclear stockpile rapidly was a "realistic requirement for coping with the military threat from the US and its satellite countries, which are getting more rampant recently," the Korean Central News Agency (KCNA) reported.

Earlier this week, North Korea condemned Australia's purchase of Virginia-class nuclear-powered submarines from the US, calling on Washington to consider the consequences of its "military adventurism that will bring a nuclear cloud to the Asia-Pacific region."