— North Korea’s army said Thursday it had received approval for a “cutting edge” nuclear strike on the United States, adding that the situation on the peninsula had reached an explosive stage.

The threat followed the North’s move Wednesday to ban South Korean workers from a joint industrial complex that has long stood as a symbol for the tenuous peace on the peninsula. South Korea’s defense minister said Seoul would consider military action if the safety of workers is put at risk.

Those moves, paired together, raised concerns in the region about the prospect for armed conflict amid uncertainty on whether the North is blustering, bluffing, or rather becoming more dangerous than it’s been since the Korean War.

In recent weeks the North has upped its hostile rhetoric while also pulling the plugs on its few lines of communication with the South, including at Kaesong Industrial Complex and a military hotline along the demilitarized border.

The statement issued Thursday followed up on a threat last month to launch preemptive nuclear strikes on the United States and its allies, including South Korea.

The North blamed Washington for its “hostile” policy and said its resentment toward the United States has reached an “irrepressible phase.”

“The moment of explosion is approaching fast,” the North said. “No one can say a war will break out in Korea or not and whether it will break out today or tomorrow.”

Some analysts say the North is using the threats as a way to raise tensions and pressure Seoul or Washington into negotiations. For new South Korean President Park Geun-hye, the next days will be critical in determining the future of Kaesong, where North and South Koreans worked side by side until Wednesday.

Experts said the North may be reluctant to close the Kaesong complex — located six miles north of the heavily fortified border. They said the North may instead hope to spark alarm from its richer neighbor, whose people typically view Pyongyang as a worrisome but far-removed threat — one unlikely to upend their own lives.

But the North’s decision to ban entry presents an immediate and “serious” obstacle to the roughly 120 South Korean businesses that operate at Kaesong, a South Korean government spokesman said.

North Korea has tried in recent weeks to boost tensions on the peninsula, nullifying an armistice agreement, declaring a “state of war” and vowing to produce new fissile material for its nuclear weapons. But the Kaesong move marks an even more forceful step, showing the North’s willingness to meddle with — and potentially lose — a cash cow that generates between $20 million and $100 million annually for the authoritarian government, according to estimates from economists.

The North banned entry to Kaesong at least once before, for a matter of days in 2009 during joint military exercises between the United States and South Korea. But officials in Seoul and Washington say the situation on the peninsula is now more volatile, with the North controlled by a relatively new leader, Kim Jong Un, and the South promising an immediate military counterstrike if provoked.

Kaesong, which opened in 2004, is the legacy of a far calmer period, when back to-back liberal governments in Seoul thought economic engagement would open the North to become more affluent and peaceful.

The complex is a bubble for capitalism, where South Korean firms — lured by tax breaks and low-interest government loans — use North Korean laborers who earn between $2 and $3 per day. But the facility has proven only half-successful, never becoming the transformative model for broader market-economy reforms that some South Korean officials once hoped for. The North Korean government takes back a bulk of the wages earned by its 50,000 workers.

The facility, producing everything from textiles to kitchen utensils, has instead become an 800-acre symbol of the strange and tenuous peace between the Koreas. Though songs praising the ruling Kim family play on the factory loudspeakers, the electricity, water and sewage systems all come from the South, as well as the technology and the meals for workers. Products are shipped back to the South, where they are then exported to Australia, China and various other countries.

When the North on Wednesday banned 179 South Koreans from making their daily cross-border trip to the site, beginning its blockade, 861 South Koreans were already at the complex, the South said. Many of those workers have so far elected to stay at the site so their companies can continue regular operations — at least for the short term.

Near the complex is a city of 200,000 that depends almost entirely on the factory. If the North closes Kaesong, the city will all but collapse economically, potentially causing social unrest among citizens with direct knowledge about capitalism and South Korea’s relative wealth.

“That would be huge burden on North Korean authorities,” said Lim Eul-chul, a professor of North Korean studies at Kyungnam University who has written a book about Kaesong.

The North’s anger is rooted in the international response to a long-range rocket launch in December and an underground nuclear test in February. Pyongyang said the moves were justified, but the United Nations punished them with tighter sanctions. In addition, the North has criticized ongoing U.S.-South Korean military drills that temporarily brought nuclear-capable stealth bombers to the peninsula.

Yoonjung Seo contributed to this report.