Tensions in the Korean peninsula escalated on Friday, with South Korea reporting that North Korea has loaded two intermediate-range missiles onto mobile launchers.

North Korea loaded two "Musudan" medium-range missiles and hid them in an unidentified facility near the country's east coast, South Korea's Yonhap news agency reported.

"Early this week, the North moved two Musudan missiles on the train and placed them on mobile launchers," a senior military official familiar with knowledge of the matter said, according to Yonhap.

The U.S. and South Korea are watching the North's activities in its east coast missile launching facility. South Korean intelligence officials believe that the North is preparing for a surprise attack by attempting to keep the missiles concealed.

"We are closely monitoring North Korea's missile preparations, but it is not yet clear when and where it will fire off a missile," South Korean defense ministry spokesman Kim Min-seok said in a briefing. "We will step up our military posture if the North's missile affects us."

Apparently, the Musudan missile can fly 3,000-4,000 kilometers and is capable of hitting a U.S. military base in Guam in the Pacific Ocean according to some estimates, although North Korea has not conducted any test launches of the missile.

White House spokesman Jay Carney told reporters on Thursday that the missiles “could not reach the U.S. mainland as threatened by Pyongyang,” yet Washington was taking “all necessary precautions,” he added.

Several media outlets had reported earlier that Pyongyang had moved its medium range missiles toward the country’s east coast, prompting the U.S. to send its advanced missile defense system and destroyers to its military base in Guam. However, it is not yet clear whether the missiles were shifted for a test or a military drill.

"South Korean and U.S. intelligence authorities have obtained indications the North has moved an object that appears to be a mid-range missile to the east coast," an anonymous South Korean source told Reuters.

South Korea also dispatched two of its 7,600-ton Aegis destroyers to its east and west coasts to counter any missile attack from the North, following the threats. Aegis destroyers are equipped with SPY-1 radar, which allows them to track hundreds of objects simultaneously from up to 1,000 kilometers away.

"If the North fires off a missile, we will trace its trajectory," a senior Navy official said.