US Ballistic Missile Submarine USS Kentucky is anchored in Busan Naval Base on July 19, 2023 in Busan, South Korea. (Gettyimages)

North Korea threatened Monday to take powerful deterrent action against what it claims is the US nuclear threat, denouncing Washington for its recent subcritical nuclear test.

The US carried out a subcritical nuclear test in Nevada last week, the third of its kind under President Joe Biden. The US said it was designed to collect "essential data" about its nuclear warheads.

An unnamed spokesman at the North's foreign ministry said North Korea cannot but reconsider the measures necessary for improving its overall nuclear deterrence posture, adding that the US is not qualified to talk about nuclear war threats from others.

North Korea "will not tolerate the creation of strategic imbalance and security vacuum in the Korean peninsula, but firmly defend its security, rights and interests through powerful deterrent action against the evolving nuclear threat from the US," the spokesman was quoted as saying by the Korean Central News Agency, without elaborating.

North Korea conducted its sixth and last nuclear test in September 2017 and enshrined its nuclear power status in its constitution in September.

Officials in Seoul and Washington have said Pyongyang may conduct its seventh nuclear test "at any time," noting the country appears to have completed all preparations for a nuclear test. (Yonhap)