North Korea has loaded two intermediate-range missiles onto mobile launchers and hidden them in an unidentified facility near the east coast, Seoul military sources said Friday, triggering speculation that the North is ready for an abrupt missile launch.

   Earlier this week, the communist state had moved the "Musudan" medium-range missiles to its east coast, prompting the United States to send its advanced missile defense system to its base on the Pacific Ocean island of Guam.

   South Korea has also sent its Aegis destroyers equipped with advanced radar systems to the East and West Seas.

   South Korean and U.S. intelligence officials have been closely monitoring the North Korean facility believed to contain the Musudan missiles on the TELs (transporter-erector-launcher). The missile can fly 3,000-4,000 kilometers and is capable of hitting the U.S. base in Guam in the Pacific Ocean.

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

   The North's concealing the missiles atop the mobile launcher platform is seen as an attempt to launch missiles in a surprise move, the official said, noting it was not clear whether the move is for a test firing or military drills.  

   The isolated communist nation has not yet conducted a test firing of the Musudan missile, which was first revealed to the international community in October 2010 during a military parade in Pyongyang.

   On Thursday, CNN reported classified images and communications intercepts showing that North Korea has moved two mobile missiles, launchers and fuel tanks to its east coast, citing an anonymous American official.

   In response to the North's military move, South Korea has sent two Aegis destroyers equipped with advanced radar systems to both of its coasts, Navy officials said.

   The 7,600-ton Aegis destroyers with SPY-1 radar, which can track hundreds of targets as far as 1,000 kilometers away, have been on standby on the east and west coasts of the Korean Peninsula to track missile launches by Pyongyang, according to a senior Navy official.

   "If the North fires off a missile, we will trace its trajectory," the official said asking for anonymity citing confidential information.

   The South Korean military is also operating the ground-based missile defense radar system Green Pine, and the early warning aircraft Peace Eye under stepped up military readiness status to prepare for a potential rocket launch, according to the officials.

   "We are closely monitoring North Korea's missile preparations, but it is not yet clear when and where it will fire off a missile,"

defense ministry spokesman Kim Min-seok said in a briefing. "We will step up our military posture if the North's missile affects us."  

   In response to media reports that the North may plan to launch a missile in the coming days or weeks, Kim said Pyongyang could pick a launching day it deems "meaningful," without elaboration.

   Outside observers see a high chance that Pyongyang may launch the missile in mid-April to celebrate the April 15 birthday of Kim Il-sung, the communist nation's late founder and the young leader Kim Jong-un's grandfather, in a move to bolster the regime's grip on power.

   Meanwhile, the defense ministry has dispatched a team of inspectors to the front-line island of Yeonpyeong to look into the border crossing by a North Korean defector across the tensely guarded western sea border.

   The 28-year-old defector, who was living in the South, slipped through radar monitoring on Wednesday night to sail across the maritime border in the Yellow Sea, sparking security concerns at a time of military tensions with the North.

   "Investigations are currently underway," Kim said. "After the inspection, we'll figure out what kind of additional measures are needed" to strengthen border security. (Yonhap)