On Tuesday, a U.S. official said that the American government believes a test launch could happen at any time and without North Korea issuing a standard notice to commercial aviation and maritime shipping that would warn planes and vessels to stay away from the missile's path.
The official, who declined to be named because of the sensitivity of the information, cautioned that most of the information comes from satellite imagery, so it's impossible to reach a definitive conclusion because the United States cannot gather information on the ground.
He said the launch could be "imminent" but also cautioned that the United States "simply doesn't know." Based on what the United States has seen, the belief is that the missiles have received their liquid fuel and are ready for launch.
Speaking at a Senate Armed Services hearing Tuesday, Locklear said the U.S. military would not want to shoot down a North Korean missile whose trajectory would send it into the open sea. But he said if a missile's path appeared to threaten a U.S. ally, such as Japan, interceptor missiles could be used to try to bring it down.
Japan poised to react 'calmly'
Japan's deployment of missile defenses in Tokyo follows similar measures taken ahead of the North's rocket launches last year. Prime Minister Shinzo Abe told reporters Tuesday that his government would do "calmly" whatever needed to be done to protect its population.
In a sign of the level of concern, however, the port city of Yokohama had to apologize for prematurely publishing a warning of a missile launch on the Twitter page of its emergency management agency. The tweet was up for about 20 minutes before being removed.
The agency said that the misleading tweet was caused by human error and that it would work on changing its system to prevent the problem from happening again.
Since the U.N. Security Council voted last month to impose new sanctions on Kim's regime over the latest North Korean nuclear test, Pyongyang has kept up a steady flow of words and acts that could give the impression of a nation heading inexorably toward conflict.
On Tuesday, it advised foreigners in South Korea to secure shelter or evacuate the country in case of hostilities on the Korean Peninsula, the latest in a string of ominous warnings.
It also kept more than 50,000 of its workers from an industrial complex jointly operated with South Korea, which had been a key symbol of cooperation between the two countries.
'Holiday atmosphere' inside North Korea
But on the same day, state media published articles that described festive events and international visits, suggesting a much less fraught situation inside North Korea.
The state-run Korean Central News Agency (KCNA) reported that various sporting events were happening or scheduled to take place to mark the 101st anniversary next week of the birth of Kim Il Sung, the founder of North Korea and the grandfather of Kim Jong Un.
"The ongoing sports tournaments make the country seethe with holiday atmosphere," KCNA said. Kim Il Sung's birthday, known as the Day of the Sun, is a major public holiday in North Korea.
The planned events include an international marathon Sunday in Pyongyang in which runners from North Korea and other countries will participate. KCNA also noted Tuesday the arrival by plane in North Korea of a delegation from the Japan-Korea Society for Scientific and Educational Interchange.
Such visits sit strangely alongside the North's warning last week to foreign diplomats in Pyongyang that it wouldn't be able to guarantee their safety in the event of a conflict.
Some North Korea watchers have observed that the regime's domestic propaganda has focused recently on efforts to promote economic development, while the bellicose threats appear targeted primarily at a foreign audience.
Varying levels of concern
The angry rhetoric has also failed to alarm South Koreans, who have lived through decades of North Korean bombast. Residents of Seoul have continued to go unflappably about their daily business.