SEOUL (Reuters) - The United States flew two nuclear-capable stealth bombers on practice runs over South Korea on Thursday, in a rare show of force following a series of North Korean threats that the Pentagon said have set Pyongyang on a dangerous path.
The drill by the two B-2 Spirit bombers - flying all the way from the United States and back - appeared to be the first exercise of its kind and showed America's ability to conduct long-range, precision strikes "quickly and at will," the U.S. military said.
The bomber flights, and the unusual public announcement of them by the U.S. military, appeared designed to send a message of Washington's resolve to North Korea amid rising tensions on the Korean peninsula.
In recent weeks, North Korea has said it cancelled an armistice agreement with the United States that ended the 1950-53 Korean War and has cut all communications hotlines with U.S. forces, the United Nations and South Korea.
North Korea has threatened South Korea with war and the mainland United States with a pre-emptive nuclear strike, although it is far from clear it has the ability to carry out the latter threat.
"The North Koreans have to understand that what they're doing is very dangerous," U.S. Defence Secretary Chuck Hagel told reporters at the Pentagon.
"We must make clear that these provocations by the North are taken by us very seriously and we'll respond to that."
The U.S. military said that its B-2 bombers had flown more than 6,500 miles (10,461 km) to stage a trial bombing raid from their bases in Missouri as part of Foal Eagle war drills being held with South Korea.
The bombers dropped inert munitions on the Jik Do Range, in South Korea, and then returned to the continental United States in a single, continuous mission, the military said.
Thursday's drill was the first time B-2s flew round-trip from the mainland United States over South Korea and dropped inert munitions, a Pentagon spokeswoman said.
'REHEARSALS FOR INVASION'
North Korea has put its armed forces on readiness to fight what it says are "hostile" war drills by the United States and South Korea, describing them as rehearsals for invasion. The U.S. says the annual drills are entirely defensive.
Victor Cha, a North Korea expert at the Center for Strategic and International Studies, said the drill fit within the context of ramped efforts by the Pentagon to deter the North from acting upon any of its threats.
Asked whether he thought the latest moves could further aggravate tensions on the peninsula, Cha, a former White House official, said: "I don't think the situation can get any more aggravated than it already is."
Despite the shrill rhetoric from Pyongyang, few believe North Korea, formally known as the Democratic People's Republic of Korea, will risk starting a full-out war.
It has also kept a joint economic zone with the South open as it generates $2 billion a year in trade from the venture, money the impoverished state can ill-afford to lose.
Still, Hagel, who on March 15 announced he was bolstering missile defences over the growing North Korea threat, said all of the provocations by the reclusive state had to be taken seriously.
"Their very provocative actions and belligerent tone, it has ratcheted up the danger, and we have to understand that reality," Hagel said, renewing a warning that the U.S. military was ready for "any eventuality" on the peninsula.
North Korea conducted a third nuclear weapons test in February in breach of U.N. sanctions and despite warnings from China, its one major diplomatic ally.
While the North has an armoury of Soviet-era Scud missiles that can hit South Korea, its longer-range missiles remain untested.
Independent assessments of its missile strike force suggest that it may have the theoretical capacity to hit U.S. bases in Japan and Guam, but the North has not tested these missiles.
Still, Hagel told reporters the North had a "significant" missile capability and defended his decision to spend nearly $1 billion bolstering American missile defence capabilities, saying the Pentagon needed to plan for potential threats.
"You only need to be wrong once," Hagel said.
"And I don't know what president or what chairman or what secretary of defence wants to be wrong once when it comes to nuclear threats."