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.
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, according to The Telegraph UK.
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".
Mattis warned that the US would never accept a nuclear north and that dictator Kim Jong-un was overmatched by American firepower.
Experts are divided about whether the unusual North Korean drills are a sign that the regime feels more threatened than before, or wants to create the perception that it is taking care of its citizens.
"I have never heard of this type of training exercises before in North Korea, but am not surprised," Chun In-bum, a recently retired South Korean three star lieutenant-general told NK News. "They must realise how serious the situation is."
But Christopher Green, a PhD candidate at University of Leiden, Germany, argued that it was unclear "whether genuine security concerns are driving this, or the wish to portray the image of a government that has concerns over security".
Defectors have spoken of frequent air raid drills during times of tension but not in recent years.
In 1994, during a confrontation with Washington over Pyongyang's nuclear ambitions, daily air raid drills reportedly took place.
In 2013, when relations with South Korea were tense, the North Koreans also fostered a sense of crisis by requesting Pyongyang vehicles to cover their roofs with camouflage netting.
Some analysts argue that fiery statements from US President Donald Trump may have created genuine fear.
At the UN General Assembly in September, Trump threatened to "totally destroy" North Korea if provoked. The US military has also ramped up military deployments near the Korean peninsula.
US keeps deployment of 'strategic assets' mysterious
Trump last month agreed to send more of the Pentagon's "strategic assets" to South Korea on a rotational basis to deter North Korean provocations, but what exactly that means remains something of a mystery, according to the Washington Post.
The US assets - typically defined as submarines, aircraft carriers, nuclear weapons, or bombers - have long been involved in the standoff that began with the 1953 Korean Armistice Agreement after open warfare subsided between the two Koreas. In a year in which North Korea has shown significant progress toward mounting a nuclear warhead on a intercontinental ballistic missile, Trump and South Korean President Moon Jae-in agreed to bolster the US presence in the region.
The Pentagon describes these forthcoming moves as the "enhanced deployment of US strategic assets in and around South Korea on a rotational basis", but it has provided few additional details. It appears they are still in the works. Marine General Joseph F. Dunford Jr, the chairman of the Joint Chiefs of Staff, said on Saturday he had just discussed the deployment of strategic assets with South Korean counterparts during two days of meetings in Seoul.
"Is it different things? No," Dunford said. "Is it doing different things at different times? Yes. And is it incorporating other capabilities on occasion? Yes."
Dunford declined to detail what might be used, but said the discussion centred on combining the 28,500 US troops based in South Korea fulltime along with annual exercises and "our occasional rotation of forces" to bolster deterrence against North Korea. The point, he said, is to demonstrate the strength in the alliance between South Korea and the US and the capability to respond militarily if necessary.
"It wasn't a specific, 'We want this or that', " Dunford said of the message the South Koreans conveyed. "It was more of a conversation about exercise cycles, patterns of deployments and so forth that would most enhance."
Mattis has been even more vague. Asked if strategic assets will stay on the South Korean Peninsula for a fixed amount of time, he declined to answer.
"Regarding our strategic assets, they are global in their positioning," he said. "They are global in their reach, and we are quite assured that they are in a position to be responsive ... So, that's all I've got to say about that."
Mattis' South Korean counterpart, Defence Minister Song Young-moo, said the two countries have agreed to expand "relevant co-operation" involving strategic assets, including studies to improve deterrence against North Korea.
Song also asked last month for the United States to consider reintroducing tactical nuclear weapons in South Korea, but the move is considered unlikely among many US military officials. In addition to it potentially putting tensions with North Korea at a new high, Moon has said he is against the idea.
Dunford spent the weekend in Hawaii following his meetings in Seoul for a three-party gathering that again included his South Korean counterpart, General Jeong Kyeong-Doo, along with their Japanese equivalent, Admiral Katsutoshi Kawano.
South Korea and Japan have had strained relations for years, dating back at least to the Empire of Japan's occupation of the Korean Peninsula during World War II and its use of so-called "comfort women", who were forced into sexual slavery for Japanese soldiers. The three nations have participated together in operations meant to be a unified message for North Korean leader Kim Jong Un.
In one example, Air Force B-1B bombers from Andersen Air Force base in Guam flew in formation Sept. 17 with fighters from all three nations before dropping live bombs on a range few dozen kilometres from the demilitarised zone separating the two Koreas. The Japanese F-2 fighters broke off from the formation and did not fly over the peninsula, but were depicted in photographs released by the Pentagon in a show of force.
The US Navy typically keeps the movements of its submarines secret, but also has periodically sent them to port in South Korea. The USS Michigan, an Ohio-class nuclear-powered ballistic missile submarine, has appeared at Busan Naval Base in South Korea at least twice this year. It is capable of carrying nuclear missiles, as well as elite Navy SEALs.
More recently, the Navy announced last week it has plans for a massive exercise involving three aircraft carriers - the USS Nimitz, the USS Theodore Roosevelt and the USS Ronald Reagan - and their associated strike groups, each of which include dozens of aircraft and thousands of sailors and Marines.
The exercise will be carried out as Trump visits South Korea, and is a rarity - no three-carrier operation has occurred since 2007, said Marine Lieutenant General Kenneth F. McKenzie Jr, the director of the Pentagon's Joint Staff. Dunford and others have effectively downplayed the significance of the timing as a coincidence, citing the length of time it takes to plan the movements of aircraft carriers.
"These three carriers are not there specifically targeting North Korea," the chairman said. "This is a routine demonstration of our commitment to the region."
The chairman did acknowledge closer attention is being paid to Pyongyang, in light of its actions.
"I think it's fair to say that all of us," he said, "Have a heightened sense of urgency for the past year and a half, and in particular, in the last couple months."