WASHINGTON -- A nuclear attack by North Korea against the US or its allies will result in the end of the country's regime, the US Department of Defense said Thursday.

In its National Defense Strategy, the department said the US will also hold North Korea responsible for any transfer of nuclear weapons or related materials and technology to other actors.

"Any nuclear attack by North Korea against the United States or its allies and partners is unacceptable and will result in the end of that regime," said the NDS.

"There is no scenario in which the Kim regime could employ nuclear weapons and survive," it added, referring to North Korean leader Kim Jong-un.

The new US defense strategy comes amid speculation that Pyongyang may soon conduct what will be its seventh nuclear test.

The North conducted its sixth and last nuclear test in September 2017.

John Kirby, spokesman for the White House National Security Council, said North Korean leader Kim Jong-un may be prepared to conduct a nuclear test at any time.

"Offensive as they are, which just causes more instability on the peninsula and contributes to a degradation in the security environment, we have said for months now that Mr. Kim could conduct another nuclear test at any moment. And we still believe that that's the case," the NSC strategic communications coordinator said in a press conference organized by the Washington Foreign Press Center.

Kirby reaffirmed US commitment to engage with Pyongyang, but said the US will continue to prepare for all contingencies at the same time.

"But again, I want to stress we are willing to sit down without preconditions and there is no reason for another test to occur," he said. "In the meantime, given that he (Kim) hasn't shown any inclination to want to talk, we have to do what we must make sure that we can defend ourselves and our allies."

Defense Secretary Lloyd Austin said the NDS is "clear eyed" about threats posed by North Korea and its evolving nuclear, missile capabilities.

"The NDS is also clear eyed about other serious threats and that includes North Korea's expanding nuclear and missile capabilities," he told a press briefing.

North Korea has launched a total of 44 ballistic missile launches this year, the largest number of ballistic missile it fired in a single year, according to US officials.

"The NDS charges us to defend the US homeland to deter strategic attacks against the United States and our allies and partners, to prepare to prevail in conflict when necessary," said Austin.

The NDS also highlights proliferation risks posed by North Korea.

"We will hold the (North Korean) regime responsible for any transfer it makes of nuclear weapons technology, material or expertise to any state or non-state actor," it said. (Yonhap)