North Korea launches what it claimed was a hypersonic missile, Jan. 5, in this photo provided by the North Korean government. AP-Yonhap

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

In its National Defense Strategy (NDS), the department said the U.S. 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 U.S. 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.