North Korea exchanged artillery fire with the South on Monday, a day after it warned it could carry out a "new form of nuclear test," the New York Times reports.
The two Koreas each sent hundreds of artillery rounds across a disputed maritime sea boundary. South Korean officials said the artillery exchange did not hurt anyone. Still, the two countries have not had such a volatile sea episode since 2010 when the North shelled an inhabited South Korean island.
Pyongyang was frustrated with the rebuke it received on Thursday from U.N. Security Council members, Reuters reported. During a close-door session of the 15-nation body, individual members castigated the North for its test-firing earlier last week of two medium-range ballistic missiles.
"It is absolutely intolerable that the U.N. Security Council ... 'denounced' the Korean People's Army (KPA)'s self-defensive rocket launching drills and called them a 'violation of resolutions,'" the North Korean Foreign Ministry said in a statement carried by official regime media.
The ministry warned that additional drills were in the offing and would involve "more diversified nuclear deterrence" that would be aimed at hitting longer range targets "with a variety of striking power."
"We would not rule out a new form of nuclear test for bolstering up our nuclear deterrence," the statement said.
The threat of a new kind of atomic test could mean the North is planning to blow up its first uranium-based nuclear device. While Pyongyang's first two underground atomic detonations used plutonium, independent analysis of the third test in 2013 could not determine whether it employed plutonium or highly enriched uranium.
Jeffrey Lewis of the James Martin Center for Nonproliferation Studies told the Wall Street Journal that Pyongyang's statement hints at the opening of a new phase in its nuclear testing program.
"The old way was that we thought of the North’s test as ‘atomic temper tantrums’ -- they’d do one-offs every few years to show us how angry they are," Lewis said. "But to me, it looks like they’re getting ready to do a lot of tests over the next few years."