China's state-controlled media on Monday cast a wary eye on remarks by North Korean leader Kim Jong-un that his country will not use its nuclear weapons unless its sovereignty is invaded.

The remarks by Kim, announced during a rare congress of North Korea's ruling Workers' Party and reported by the North Korean media on Sunday, reaffirmed the North's bid to become a nuclear weapons state, dashing hope that the young leader might chart a difference course on the country's nuclear weapons program.

"Our republic is a responsible nuclear state that, as we made clear before, will not use nuclear weapons first unless aggressive hostile forces use nuclear weapons to invade our sovereignty," Kim was quoted as saying by North Korea's state media.

The Global Times newspaper, controlled by China's ruling Communist Party, said in an editorial that North Korea's isolation would deepen unless the North gives up its nuclear ambitions.

"International society is firmly against Pyongyang's nuclear program," the editorial reads. "The external world believes that North Korea is playing a different card to test its effectiveness, and its ultimate goal is to legitimize its nuclear development."

"Major countries will not change their stance to recognize North Korea as a nuclear state. As long as Pyongyang resists giving up its nuclear weapons, normalizing relations with the outside world will be highly unlikely," it said.

"To begin with, Kim's declaration was made from the perspective that North Korea is now a nuclear state," it said.

"The international community has not yet acknowledged North Korea as a nuclear nation, so therefore the latter's attitude has not changed, and neither has its biggest contradiction with the outside world been resolved," it said.

However, the Chinese paper interpreted the remarks by Kim as a "relaxed manner that might buffer the current touch-and-go tensions."

China's official Xinhua news agency also took note of Kim's pledge.

Citing some Chinese experts on the Korean Peninsula, the Chinese news agency reported that the pledge by Kim was different from the North's previous threats that hinted the country could use its nukes to strike out at its enemies. (Yonhap)