North Korea on Thursday warned the incoming Donald Trump administration will have to acknowledge it as a nuclear state, as the South said the maverick billionaire had pledged to protect it.

The United States maintains it cannot accept North Korea as a nuclear power, despite it conducting five nuclear tests -- including two in 2016 -- and has pushed harsh international sanctions against the Pyongyang regime.

"If there is anything the Obama administration has done... it has put the security of the US mainland in the greatest danger," said an editorial carried by North Korea's ruling party newspaper Rodong Sinmun.

"It has burdened the new administration with the difficulty of facing the Juche nuclear state," it said, referring to the North Korean ideology usually translated as "self-reliance".

The editorial, which did not mention Trump by name, follows growing calls for the United States to change tack on North Korea, with US Director of National Intelligence James Clapper last month labelling attempts to denuclearise the North a lost cause.

President Barack Obama has made talks with the North conditional on Pyongyang first making some tangible commitment towards denuclearisation, but Thursday's editorial called the goal an "outdated illusion".

Although Trump has not laid out a clear direction for his policy on North Korea, he has indicated that he would be open to negotiations with its leader Kim Jong-Un in the US to talk him out of his nuclear ambitions.

Trump caused consternation during his campaign when he threatened to withdraw the troops unless Seoul paid more for their upkeep, and suggested South Korea and Japan develop their own nuclear weapons to counter threats from Pyongyang.

But in a phone call with South Korean President Park Geun-Hye on Thursday, Trump vowed that US commitment on protecting its ally against the North "will not waver".

"We are going to be with you 100 percent," Trump said, according to a statement from South Korea's Blue House.

"We will be steadfast and strong with respect to working with you to protect against the instability in North Korea," Seoul quoted him as saying.

North Korea has been hit by five sets of UN sanctions since it first tested a nuclear device in 2006.

After Pyongyang carried out its fourth nuclear test in January, the Security Council adopted the toughest sanctions resolution to date, targeting North Korea's trade in minerals and tightening banking restrictions.

Council members are currently debating a fresh resolution after the North's fifth nuclear test in September.

According to Security Council diplomats, the negotiations are focused on closing loopholes and zeroing in on North Korea's nuclear and ballistic missile technology industry.