The U.N. Security Council recently punished North Korea for a rocket launch in December that the U.N. and Washington called a cover for a banned long-range missile test. Pyongyang said it was a peaceful launch of a satellite into space. In condemning that launch, the council demanded a stop to future launches and ordered North Korea to respect a ban on nuclear activity or face ‘‘significant action’’ by the U.N.
It wasn’t immediately clear to outside experts whether the device exploded Tuesday was small enough to fit on a missile. A successful test would take North Korean scientists a step closer to building a nuclear warhead that could reach U.S. shores — seen as the ultimate goal of North Korea’s nuclear program.
Uranium would be a worry because plutonium facilities are large and produce detectable radiation, making them easier for outsiders to find and monitor. However, uranium centrifuges can be hidden from satellites, drones and nuclear inspectors in caves, tunnels and other hard-to-reach places. Highly enriched uranium also is easier than plutonium to engineer into a weapon.
‘‘North Korea will want to send a message that its nuclear and missile issues cannot be resolved with sanctions and that high-level talks with the U.S. are necessary,’’ said Cheong Seong-chang, an analyst at the private Sejong Institute in South Korea, referring to the possibility of another nuclear or missile test.
Despite tensions, he predicted U.S.-North Korea diplomatic talks could occur later this year.
‘‘The biggest U.S. concern is whether the North has made progress in its uranium enrichment program. It’s a matter of nuclear proliferation. To resolve this, the U.S. cannot help but talk with North Korea,’’ he said.
Associated Press writers Sam Kim in Seoul, South Korea, Eric Talmadge in Tokyo and Edith M. Lederer at the United Nations contributed to this report.