The threat of a new North Korean missile launch is "considerably high," South Korea's foreign minister has warned.
It is expected to be medium-range, capable of reaching Japan, Yun Byung-se said. Earlier, the Defence Ministry said preparations appeared complete, and the launch could take place at any time.
Mr Yun said Seoul was bracing for the test-fire of a ballistic missile dubbed "Musudan" by foreign experts after the name of the north-eastern village where North Korea has a launch pad. Experts said the Musudan is built to reach the US territory of Guam as well as US military installations in Japan.
A test-firing of the Musudan missile would violate UN Security Council resolutions banning North Korea from nuclear and missile activity, and escalate tensions.
Japan has deployed PAC-3 missile interceptors in key locations around Tokyo.
North Korea has not announced launch plans but has told foreign diplomats in Pyongyang that they will not be able to guarantee their safety. It has also urged tourists in South Korea to take cover, warning that nuclear war is imminent. However, most diplomats and foreign residents appeared to be staying put.
The threats are largely seen as rhetoric and an attempt by North Korea to scare foreigners into pressing their governments to pressure Washington and Seoul to change their policies toward Pyongyang, as well as to boost the military credentials of North Korea's young leader, Kim Jong Un.
On the streets of Pyongyang, the focus was less on preparing for war and more on beautifying the city ahead of the nation's biggest holiday, the birthday of its founder Kim Il Sung. North Korea sporadically holds civil air raid drills during which people practice blacking out their windows and seeking shelter. But no such drills have been held in recent months, locals said.
Last year, the days surrounding the centennial of the birth of Kim Il Sung, grandfather of the current ruler, was marked by parades of tanks, goose-stepping soldiers and missiles, as well as the failed launch of a satellite-carrying rocket widely believed to be a test of ballistic missile technology. A subsequent test in December went off successfully, and that was followed by the country's third underground nuclear test on February 12 this year, possibly taking the regime closer to mastering the technology for mounting an atomic bomb on a missile.
The resulting UN sanctions and this spring's annual US-South Korean military drills have been met with an unending string of threats and provocations from the North.