The two ballistic missiles North Korea tested a week ago could carry nuclear warheads and would be hard to intercept with South Korea’s missile defense systems, a local security think tank said Tuesday in its latest report.

“They could put a nuclear warhead on each KN-23,” the Sejong Institute said, referring to the missiles. The report cited experts including Jefferey Lewis of the California-based Middlebury Institute of International Studies. He said the North could mount nuclear warheads.

But the North has yet to fully miniaturize nuclear warheads so the missile carrying them could fly unhindered on its projected trajectory, according to the report. The more the warheads weigh, the shorter the distance the missile can fly.

“North Koreans could make a warhead as light as 400 kilograms when the US and Russia can reduce it to as much as 110,” the report said. The UN and Japan had officially acknowledged the North had the technology to make warheads small.

The report said the KN-23 could neutralize South Korea’s missile defense systems – a multilayered shield where the Patriot and Terminal High Altitude Area Defense systems target hostile fire at low and high altitudes, respectively. The KN-23 flies between 40 and 50 kilometers high, in a gap neither system can fully cover.

But the report said the missile has drawbacks because it could give false signals. A KN-23 attack could be understood as a nuclear strike as opposed to a conventional strike, in which case North Koreans would have to expect a full-on nuclear retaliation, even if that was not what they had wanted.

By Choi Si-young (siyoungchoi@heraldcorp.com)