The senior Defence Ministry official also said that North Korea has completed preparations for a missile test that could come "any day".
The official, who spoke on condition of anonymity, said the North's military is capable of conducting multiple missile launches involving Scud and medium-range Rodong missiles, as well as a missile transported to the east coast recently.
The warning came as Pyongyang prepared to mark the April 15 birthday of its founder Kim Il-sung.
The date is historically a time when it seeks to draw the world's attention with dramatic displays of military power.
Admiral Samuel Locklear, the commander of US forces in the Pacific region, said the US military also believed the North had moved an unspecified number of Musudan missiles to its east coast.
An Obama administration official, speaking on condition of anonymity, told the Reuters news agency "our working assumption is that there are two missiles that they may be prepared to launch".
Ban Ki-moon, UN secretary general, who once served as South Korean foreign minister, said he is "deeply concerned and troubled" at the level of tension in the peninsula.
"If any small incident caused by miscalculation or misjudgement, it may create an uncontrollable situation," Ban said.
Yun Byung-se, the South Korean foreign minister, told a parliamentary hearing in Seoul that he was working through diplomatic channels in an attempt to rein in Pyongyang.
China is North Korea's only major ally, although it backed recent United Nations resolutions against Pyongyang, and Moscow was a supporter of North Korea as the Soviet Union.
Russian Foreign Minister Sergei Lavrov warned on Wednesday against stoking the North Korea crisis with military manoeuvres, but stressed Wednesday that Moscow and Washington had a common stand.
"On North Korea we have no differences with the United States," Lavrov told journalists as he met with US Secretary of State John Kerry. "One just shouldn't scare anyone with military manoeuvres and there's a chance that everything will calm down."
South Korea raises alert status
South Korea has raised its military alert status, a senior military official has said, as tensions remain high on the Korean peninsula.
10 Nisan 2013 Çarşamba 08:44
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