Pyongyang has conducted another record-breaking string of sanctions-defying launches this year, including test-firing the country's first solid-fuel ballistic missile this month -- a key technical breakthrough for Kim's military.

Seoul, Washington and the United Nations have all criticised the tests, and this week G7 foreign ministers called for the "complete, verifiable, and irreversible abandonment of (North Korea's) nuclear weapons".

North Korean foreign minister Choe Son Hui slammed the "extremely interventionist" statement, saying the G7 were "malignantly pulling up" her country's "legitimate exercise of its sovereignty".

"The position of the DPRK as a world-class nuclear power is final and irreversible," Choe said in a statement carried by the official KCNA, referring to North Korea by the initials of its official name.

Choe said the "G7, a closed group of a handful of egoistic countries, does not represent the just international community but serves as a political tool for ensuring the US hegemony."

Kim had already declared the North an "irreversible" nuclear power in September last year, effectively ending the possibility of denuclearisation talks.

Washington and Seoul have ramped up defence cooperation in response, staging joint military exercises with advanced stealth jets and high-profile US strategic assets.

North Korea views such exercises as rehearsals for invasion and again described them last week as "frantic" drills "simulating an all-out war against" Pyongyang.

"It is anachronistic to think that the right to and capability for nuclear strike is exclusive to Washington," Choe said Friday.

"We will never seek any recognition and approval from anyone as we are satisfied with our access to the strength for a tit-for-tat strike against the US nuclear threat."