North Korea unveils new nuclear warheads

STORY: North Korea unveiled some new, smaller nuclear warheads on Tuesday (March 28).

And vowed to produce more weapons-grade nuclear material to expand the country's arsenal, state media KCNA said.

The broadcaster released these photos of the warheads, dubbed Hwasan-31s, as leader Kim Jong Un visited the Nuclear Weapons Institute.

Experts say the images could indicate progress in miniaturizing warheads that are powerful yet small enough to mount on intercontinental ballistic missiles capable of striking the U.S.

KCNA said Kim Jong Un claimed the enemy of the country's nuclear forces is not a specific state or group - but "war and nuclear disaster themselves."

Adding that the policy of expanding the arsenal is solely aimed at defending the country.

North Korea has been ramping up tensions in recent days.

It fired short-range ballistic missiles on Monday, conducted a nuclear counterattack simulation last week against the U.S. and South Korea, and also testing a nuclear-capable underwater attack drone again on March 25-27.

South Korean President Yoon Suk Yeol said North Korea does not deserve "a single penny" of economic aid while pushing for nuclear development, his spokesman said.

A South Korean military spokesman said that additional tests and analysis would be needed to verify whether the North's new warheads are deployable, but that its report on the underwater drone was likely "exaggerated and fabricated."

Also on Tuesday, a U.S. carrier strike group led by the USS Nimitz docked at the Busan naval base in South Korea after conducting joint maritime drills.

It was the carrier's first visit in nearly six years - intended to improve U.S. extended deterrence given the North's evolving threats, South Korea's navy said.