North Korea has positioned two mobile missile launchers on the country's east coast, senior Pentagon officials tell Fox News -- movement that comes as Defense Secretary Chuck Hagel warned North Korea is "skating very close to a dangerous line."
The senior Pentagon official told Fox News that a test of the Musudan missiles could occur "at any time." If the North Koreans proceed, it would be the first mobile test of this specific intermediate-range missile, which has a range of 2,500 miles.
South Korea has deployed three naval destroyers, an early warning surveillance aircraft and a land-based radar system, a Defense Ministry official said in Seoul, speaking on condition of anonymity in line with department rules.
Japan has deployed PAC-3 missile interceptors in key locations around Tokyo, while the South Korean and U.S. militaries raised their level of surveillance.
Amid the tensions, people in North Korea's capital Pyongyang began celebrating a series of April holidays, including the first anniversary Thursday of their leader's appointment as head of the ruling Worker's Party.
The fact that this would be their first test is giving military leaders an added layer of uncertainty about the potential for an unintended mistake.
Separately, Hagel and Joint Chiefs Chairman Gen. Martin Dempsey addressed the North Korean crisis during a press briefing Wednesday afternoon. They said America and its allies want to ratchet down the tensions but Kim Jong Un's regime has made it difficult.
"North Korea has been, with its bellicose rhetoric, with its actions ... skating very close to a dangerous line. Their actions and their words have not helped defuse a combustible situation," Hagel said.
Reiterating statements made by America's top Pacific commander on Capitol Hill a day earlier, Hagel said the U.S. is "fully prepared to deal with any contingency, any action that North Korea may take."
"We have every capacity to... protect this country and our allies," Hagel said.
The comments come after South Korea's foreign minister told lawmakers in his country that the prospect of a North Korean missile launch is "considerably high."
Pyongyang is preparing to mark the April 15 birthday of its founder, historically a time when it seeks to draw the world's attention with dramatic displays of military power.
The missile is expected to be a medium-range Musudan missile with a range of 2,180 miles capable of flying over Japan, Foreign Minister Yun Byung-se told lawmakers in Seoul. Earlier a Defense Ministry official said preparations appeared to be complete, and that the launch could take place at any time.
North Korean officials have not announced plans to launch a missile, but have told foreign diplomats in Pyongyang that it will not be able to guarantee their safety starting Wednesday. It has also urged tourists in South Korea to take cover, warning a nuclear war was imminent. However, most diplomats and foreign residents appeared to be staying put.
The European Union said there was no need for member states to evacuate or relocate their diplomatic missions, but called on North Korea to "refrain from further provocative declarations or action."
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.
But officials have warned that a provocation from North Korea that goes too far could spark a broader conflict, particularly by goading South Korea into responding militarily. Such a conflict would likely draw in the U.S. and its allies.
The Obama administration in recent days has eased off its high-visibility demonstrations of military power -- like flying B-2 bombers over the region.
The U.S. delayed a scheduled missile test due to tensions in the region. But officials insist the U.S. military is prepared to deal with any threat from North Korea.
Fox News' Justin Fishel and The Associated Press contributed to this report.