North Korea stated on Monday that a recent subcritical nuclear test conducted by the United States has escalated tension in the international nuclear arms race. The state KCNA news agency reported that North Korea vowed to take necessary measures to enhance its nuclear deterrence posture in response.

The U.S. Department of Energy has said that its National Nuclear Security Administration conducted a subcritical experiment at its Nevada test site. This experiment aimed to gather data to bolster the reliability and effectiveness of nuclear warheads.

"To cope with the strategic instability in the region and the rest of the world caused by the U.S. unilateral action, (we) cannot but reconsider the measures necessary for the improvement of the overall nuclear deterrence posture within the range of its vested sovereign right and possible options," KCNA said.

It did not elaborate on what measures it would consider.

Subcritical nuclear tests do not involve a nuclear explosion and do not trigger a fissile chain reaction. The United States, a signatory to the global nuclear test ban treaty, ceased nuclear explosion tests in 1992.

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, although South Korean officials have stated that there are no indications of an imminent test.

North Korea is under U.N. Security Council sanctions for its nuclear tests and ballistic missile development.

Image source: AP