North Korea on Thursday threatened unspecified retaliation after the US flew long-range bombers over South Korea during training with its forces, which North Korea views as practice for an attack against it. The U.S. flew the B-1B bombers Tuesday during an aerial drill with other US and South Korean fighter jets. South Korea's Defense Ministry had said the training was meant to show the two countries' combined deterrence capability against North Korea's advancing nuclear program.

The U.S. and South Korea routinely hold joint military exercises they describe as defensive in nature. But North Korea views them as an invasion rehearsal and is particularly sensitive to the U.S. mobilization of strategic assets such as long-range bombers, aircraft carriers and nuclear-powered submarines.