North Korea has allegedly developed a miniature warhead that can be fitted into a ballistic missile. The claim, made by the country’s leader Kim Jong-un at a meeting with nuclear researchers, follows threats of a “preventive nuclear strike” on the US.

“The nuclear warheads have been standardized to be fit for ballistic missiles by miniaturizing them,” Kim said on Wednesday, as quoted by KCNA, North Korea’s official state news agency. He also praised the scientists, calling them the party’s “nuclear combatants.”

Kim noted that the primary function of North Korea’s nuclear arsenal is to “deter a nuclear war,” adding that the most effective way to prevent such a conflict is to “bolster up the nuclear force both in quality and quantity.”

Kim also reiterated a statement that he had made on the right of North Korea to use preemptive nuclear strikes as a defensive measure against possible aggression, saying that the prerogative to make such a move was “by no means a US monopoly.” He added that if the US “threaten its sovereignty and right to existence,” the North would “never hesitate to make a preemptive nuclear strike.”

The UN Security Council approved a new resolution on North Korea last Wednesday that significantly expands the existing sanctions on the country. The new round of restrictive measures include inspection of all cargo en route to and from the country, as well as a ban on exporting items that may contribute to the operational capabilities of North Korea’s armed forces.

The new sanctions were imposed in response to Pyongyang’s recent weapons tests. On January 6, the North claimed it had conducted an underground explosion of a hydrogen bomb. On February 7, Pyongyang successfully launched a long-range rocket that carried an earth observation satellite into orbit.

Just hours after the new package of sanctions was introduced, the North reportedly launched six short range missiles into the Sea of Japan, drawing concerned reactions from the international community.

“It means that they’re not drawing the proper conclusions yet,” said Russia’s Ambassador to the UN, Vitaly Churkin, in commenting on the developments.

The Russian Foreign Ministry issued a statement on Monday strongly condemning North Korea’s nuclear saber rattling.

“We consider the threatening statements to carry out some kind of ‘preventive nuclear strikes’ against their opponents absolutely unacceptable. Pyongyang must realize that North Korea thereby definitively pits itself against the international community, providing the international legal basis for the use of military force against it, in accordance with the right of states to self-defense written in the UN Charter,” reads the statement.