NORTH Korea’s threat to detonate an H-bomb over the Pacific seems to have been taken seriously as the US readies for a huge missile defence drill.

North Korea has been conducting rare mass evacuation and black out drills throughout the country in preparation for war, it emerged this weekend.

Multiple sources told NK News that the drills have taken place in secondary and tertiary cities and towns, particularly along the east coast, but not in the capital city, Pyongyang.

South Korean military officials described the rehearsal as the first of its kind, and added “they must realise how serious the situation is”.

State media continued to ramp up threats of war, promising a show of “powerful show of military strength”.

The revelation comes during a time of heightening tensions between the hermit state and the US after a series of nuclear and missile tests, including an intercontinental ballistic missile (ICBM) capable of striking mainland America.

The threat of nuclear missile attack by North Korea is accelerating, US Defence Secretary Jim Mattis said on Saturday during a trip to the South Korean capital, Seoul, to meet his counterpart, Defence Minister Song Young-moo.

“North Korea has accelerated the threat that it poses to its neighbours and the world through its illegal and unnecessary missile and weapons programmes,” he said, adding that US-South Korean military and diplomatic collaboration had taken on “a new urgency.”

Mr Mattis warned that the US would never accept a nuclear north and that dictator Kim Jong-un was overmatched by American firepower.

Daily Star Online reports that the Pentagon is readying to exercise at their base in the Reagan Test Site in the Pacific.

US forces are believed to be running the drill from between today and November 4 – testing their capabilities to shoot down missiles.

Warnings are in place for pilots urging them to stay away from the network of atolls around the Marshall Islands.

The Federal Aviation Administration has issued a warning for the area telling planes to stay way.

It warned “deadly force” may be used against pilots of breach airspace around the Kwajalein Atoll.

Tensions between North Korea and the US have spiked this year as US General James Mattis warned Kim of a “massive military response” if he crosses the line.

The NOTAM alert is in force from today until November 4.

Dummy missiles will be launched by the US, and then shot down using interceptor weapons in a show of force.

It comes as Kim Jong-un has promised to detonate a nuclear missile over the Pacific Ocean.

North Korea’s top diplomat has promised the threatened the warning must be taken “literally”.

US missile defence forces tested interceptors over the range back in May following a North Korean missile launch.

At the time officials denied it was in reaction to Kim’s actions, claiming it had been planned for “years”.