The move follows North Korea’s repeated tests in recent months of mid-range ballistic missiles.
Most tests have ended in failure, but the apparent success of the sixth test last week alarmed the region.
A North Korean propaganda channel has published a video showing a missile allegedly targeting the US territory of Guam in the northwestern Pacific.
The footage was released just days after Pyongyang carried out a test launch of Musudan missiles theoretically capable of flying more than 3000km.
South Korean and US officials said the first rocket failed over the Sea of Japan but a second missile was test-fired hours later, and reportedly flew for 400km before it fell.
It comes as the United States, Japan and South Korea held their first trilateral missile defence drill off Hawaii.
Officials said the exercise, dubbed “Pacific Dragon”, was aimed at countering the growing nuclear threat from North Korea.
North Korea said the drills were “military provocation”.
State media said the US and other “hostile forces” were a “constant threat” to North Korean security and reinforced its commitment to pursuing ballistic and nuclear weapons.
The US military said Pacific Dragon would enhance the “already strong relationship of all three nations participating”.
No missiles were fired, said the US Third Fleet, but each country tested its Aegis Ballistic Missile Defence System and tested communications and data collection.
The Aegis system allows warships to shoot down enemy ballistic missiles while they are still in space, before there is any danger of causing any damage.
North Korea is banned by UN resolutions from any use of ballistic missile technology. - PNC