South Korea said on Wednesday there was "very high" probability that North Korea, engaged in weeks of threats of war, would launch a medium-range missile at any time as a show of strength despite diplomatic efforts to soften its position, reported Reuters.
Foreign Minister Yun Byung-se said South Korea had asked China and Russia to intercede with the North to ease tension that has mounted since the U.N. Security Council slapped fresh sanctions on Pyongyang after a new nuclear arms test last month.
But all was calm in the South Korean capital, Seoul, long used to North Korean invective under its 30-year-old leader Kim Jong-un. Offices worked normally and customers crowded into city-center cafes.
Seoul stocks edged up 0.77 percent from a four-and-a-half-month low hit earlier this week, though trading was light with threats from the North still clouding the picture. The won currency gained 0.3 percent.
Other officials in Seoul said surveillance of North Korean activity had been enhanced. Missile transporters had been spotted in South Hamgyong province along North Korea's east coast - possible sites for a launch.
North Korea observes several anniversaries in the next few days and they could be pretexts for military displays of strength. These include the first anniversary of Kim's formal ascent to power, the 20th anniversary of rule by his father Kim Jong-il, who died in 2011, and the birth date next Monday of his grandfather, state founder Kim Il-Sung.
The near-daily threats to South Korea and the United States of recent weeks were muted in state media on Wednesday, with the focus largely on the festivities lying ahead.
A report by the KCNA news agency said North Koreans were "doing their best to decorate cities". Another dispatch related a "production upsurge" in the coal, steel, iron and timber industries, with figures showing that the quarterly plan set by authorities had been "overfulfilled".
In Washington, Admiral Samuel Locklear, the commander of U.S. forces in the Pacific region, also said the U.S. military believed North Korea had moved an unspecified number of Musudan missiles to its east coast.
The Musudan can reach targets at a distance of 3,500 km (2,100 miles) or more, according to South Korea, which would put Japan within range and may even threaten Guam, home to U.S. bases. South Korea can be reached by the North's short-range Scud missiles.