South Korea's spy agency says North Korea looks as if it's getting ready for a missile or nuclear test.

North Korea has threatened to detonate a nuclear missile over the Pacific, which could poison the ocean or lead to a strong US response.

North Korea's usual test site for nuclear devices seems damaged but still accessible.



South Korea's intelligence service on Thursday warned that it saw "active movement" at North Korea's missile research facility and that the world should expect more nuclear and missile testing from Pyongyang, according to Yonhap News.

"The North will carry out additional nuclear tests and continue to push for the development of miniaturized, diversified nuclear warheads," South Korea's National Intelligence Service said, according to lawmakers who spoke with Yonhap.

Additionally, the spy agency noted that North Korea had some trouble with its nuclear test site, with a recent nuclear blast causing landslides and cave-ins that apparently restricted access to the site.

On Tuesday, Japan's Asahi TV quoted a North Korean source as saying that cave-ins in tunnels at the nuclear test site caused the death of up to 200 workers.

South Korea's NIS, however, maintained that North Korea still had access to the site via an alternative tunnel, and North Korea denied that the workers were killed.

North Korea has recently floated the idea of conducting above-ground or atmospheric testing instead.

A CNN reporter quoted a North Korean official as saying the US should take "literally" its threat to detonate the "strongest hydrogen bomb test over the Pacific Ocean."

Separately, North Korea has threatened to launch a salvo of missiles at the US territory of Guam.

To do so, North Korea would have to fire a medium- to long-range missile. North Korea hasn't tested a missile in over a month, its longest pause since it began launching missiles in February.

The US maintains a large naval presence in the Pacific with advanced ballistic-missile-defense capabilities.

Experts have told Business Insider that if the US assesses that North Korea may fire a ballistic missile with a nuclear warhead, the military may look to shoot the missile down.