North Korea has enshrined nuclear weapons in its constitution, state media said on Thursday.

The country's rubber-stamp parliament unanimously adopted "the crucial agenda item for formulating [North Korea's] policy on the nuclear force as the basic law of the state," the state-run Korean Central News Agency (KCNA) reported.

"The DPRK's nuclear force-building policy has been made permanent as the basic law of the state, which no one is allowed to flout with anything," said leader Kim Jong Un, using the acronym for the country's official name.

Kim added that it was "very important" to "accelerate the modernization of nuclear weapons in order to hold the definite edge of strategic deterrence."

North Korea's nuclear ambitions

The amendment comes a year after North Korea officially "irreversibly" declared itself to be a nuclear state and enshrined in law the right to use preemptive nuclear strikes to protect itself.

Kim returned from a rare trip to Russia last week where he and Russian President Vladimir Putin agreed to boost military cooperation.

South Korea and the United States have expressed concern that North Korea could seek technical assistance from Russia for its nuclear missile programs while Moscow looks to source ammunition for its invasion of Ukraine.

South Korea's President Yoon Suk Yeol warned Pyongyang against using nuclear weapons on Tuesday as Seoul staged its first large-scale military parade in a decade.

Pyongyang's last nuclear test was in 2017, but it has tested intercontinental ballistic missiles with mock nuclear warheads in recent months.