In a show of force following weeks of North Korean bluster, the U.S. on Thursday took the unprecedented step of announcing that two of its nuclear-capable B-2 bombers joined joint military drills with South Korea, dropping dummy munitions on an island range.

The announcement is likely to further enrage Pyongyang, which has already issued a flood of ominous statements to highlight displeasure over the drills and U.N. sanctions over its nuclear test last month. But there were signs Thursday that it is willing to go only so far.

A North Korean industrial plant operated with South Korean know-how was running normally, despite the North’s shutdown a day earlier of communication lines ordinarily used to move workers and goods across the border. At least for the moment, Pyongyang was choosing the factory’s infusion of hard currency over yet another provocation.

U.S. Forces Korea said in a statement that the B-2 stealth bombers flew from a U.S. air base in Missouri and dropped dummy munitions on the South Korean island range before returning home. It was unclear whether America’s stealth bombers were used in past annual drills with South Korea, but this is the first time the military has announced their use.

The statement follows an earlier U.S. announcement that nuclear-capable B-52 bombers participated in the joint military drills.

North Korea sees the military drills as part of a U.S. plot to invade and becomes particularly upset about U.S. nuclear activities in the region. Washington and Seoul say the drills are routine and defensive.

North Korea has already threatened nuclear strikes on Washington and Seoul in recent weeks. It said Wednesday there was no need for communication in a situation “where a war may break out at any moment.” Earlier this month, it announced that it considers void the armistice that ended the Korean War in 1953.

But Pyongyang would have gone beyond words, possibly damaging its own weak finances, if it had blocked South Koreans from getting in and out of the Kaesong industrial plant, which produced $470 million worth of goods last year.

South Korean managers at the plant reported no signs of trouble Thursday.

Analysts see a full-blown North Korean attack as extremely unlikely, though there are fears of a more localized conflict, such as a naval skirmish in disputed Yellow Sea waters. Such naval clashes have happened three times since 1999.

The Kaesong plant, just across the heavily fortified Demilitarized Zone that separates the Koreas, normally relies on a military hotline for the governments to coordinate the movement of goods and South Korean workers.

Without the hotline, the governments, which lack diplomatic relations, used middlemen. North Korea verbally approved the crossing Thursday of hundreds of South Koreans by telling South Koreans at a management office at the Kaesong factory. Those South Koreans then called officials in South Korea.

Both governments prohibit direct contact with citizens on the other side, but Kaesong has separate telephone lines that allow South Korean managers there to communicate with people in South Korea.

North Korea’s latest threats are seen as efforts to provoke the new government in Seoul, led by President Park Geun-hye, to change its policies toward Pyongyang. North Korea’s moves at home to order troops into “combat readiness” also are seen as ways to build domestic unity as young leader Kim Jong Un, who took power after his father’s death in December 2011, strengthens his military credentials.