As the United Nations Security Council met to discuss Pyongyang's Tuesday firing of an intermediate-range ballistic missile over Japan, North Korea said in a statement that such launches were "the just counteraction measures of the Korean People's Army on South Korea-US joint drills".

Security allies Washington and Seoul have ramped up joint military drills in recent weeks, including large-scale naval manoeuvers and anti-submarine exercises.

North Korea said this was what was "escalating the military tensions on the Korean peninsula".

Pyongyang's statement also slammed the US decision on Wednesday to redeploy the nuclear-powered USS Ronald Reagan to the Korean Peninsula for a second visit in less than a month.

"The DPRK is watching the U.S. posing a serious threat to the stability of the situation on the Korean peninsula and in its vicinity by redeploying the carrier task force in the waters off the Korean peninsula," it said, using the acronym for North Korea's official name.

Global condemnation has mounted over Pyongyang's likely longest-ever test Tuesday, which the South Korean and US militaries responded to on Wednesday with a volley of missiles into the sea.

Pyongyang fired two short-range ballistic missiles on Thursday, its sixth launch in less than two weeks and the latest in a record year of sanctions-busting weapons tests by the isolated regime.

In September, North Korea revised its nuclear laws, with leader Kim Jong Un declaring his country an "irreversible" nuclear power.