U.S. officials suspect that North Korea may be preparing for a test of its Musudan medium-range missile after seeing evidence of it being transported to North Korea's eastern coast. Such a launch would be the latest in a series of provocations by North Korea in recent weeks.

Earlier Thursday, South Korea's defense minister told his nation's lawmakers that a North Korean missile with "considerable range" had been transported to that country's eastern coast. Defense Minister Kim Kwan-jin said he could not explain the movement and added that the missile was not capable of reaching the United States.

Ng Han Guan/AP Photo

U.S. officials have identified the missile as a mobile-launched Musudan missile estimated to have a range of between 1,800 and 2,500 miles that could put U.S. military bases in Okinawa and Guam within its range.

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The officials said that, two days ago surveillance satellites detected the movement by train of a Musudan mobile launcher as well as fuel and equipment needed for a missile launch.

One official said it is possible that as many as two missiles could be readied for a potential launch because there were more missile components spotted than might be needed if only one missile was being launched.

The U.S. is trying to locate the location on the eastern coast where the launcher and missile components are currently located.

The officials said there is speculation that a missile test could be in the works and that it could occur soon. Unlike long-range missiles, which can spend weeks on a launch pad in preparation for a launch, mobile-launched missiles can be launched fairly quickly and with little warning.

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The Musudan is a medium-range missile that has never been tested before, though it has been publicly paraded by North Korea in the past. U.S. officials have been expecting it to be tested at some point over the past few years.

A U.S. official said that, so far, North Korea has not provided a notice to mariners about a potential missile launch. During previous long-range launches, the North Koreans have listed advance warnings to mariners and aviators. In addition to serving as safety warnings that a missile may land near a body of water, they have also served as indicators of a possible launch. The official said launching this missile without such an advance advisory would be seen as a provocation.

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One of the officials said there is also concern about how Japan might react if a North Korean missile were to overfly its territory. Placing the Musudan on the eastern coast indicated the trajectory might take it over Japan. Last December, in advance of North Korea's long-range missile test that month, the Japanese government gave orders to its military shoot down a missile should it appear to be headed for Japanese territory.

That did not happen, as the Unha 3 missile was launched on a southward trajectory away from the Korean Peninsula. Japan has both land-based and ship-based missile interceptors like the ones aboard U.S. Navy ships.

In light of North Korea's recent threats to launch missiles at the United States, the Pentagon has assigned two of its missile-defense-capable Navy destroyers to provide missile defense if needed.

On Tuesday, the Pentagon confirmed the destroyers USS John S McCain and USS Decatur had been sent to pre-determined locations in the western Pacific.

The USS Decatur will soon be replaced by the destroyer USS Fitzgerald so that it can return to its homeport of San Diego after a seven-month deployment.

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Japan and South Korea both have short-range air missile defense systems, the U.S. Navy ships can provide backup if the trajectory is beyond that range and pose a threat to other partners in the region and U.S. territory.

In the wake of North Korea's missile threat on Wednesday, the Pentagon announced that it was sending a land-based missile defense system to Guam.

North Korea also has a mobile-launched, long-range missile known as the KN-08. North Korea has never tested the missile, but it is of particular concern because it can be launched with little warning and is believed to be able to reach parts of the United States.

One official said there has been no worrisome activity related to the KN-08.