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North Korea test fired two short-range ballistic missile off the country's eastern coast shortly before midnight Sunday, nearly two days leader Kim Jong Il is believed to have died, a senior U.S. defense official told Fox News.

The unidentified senior official said the launch was "not viewed as threatening or destabilizing to the region," but added it's unclear that it was not related to the dictator's death and impending regime change.

The most likely explanation, some U.S. officials told Fox News, is that the "pre-planned" launch might have been moved up to coincide with the regime change to project a message of "we're still here" to regional powers and the world.

The missiles were the North Korean equivalent of Russian SS-21 missiles, which were fired from the back of a vehicle. They have a range of roughly 75 miles, a senior U.S defense official told Fox News.

The announcement of Kim's death has led to "no change to US force posture," the official said. There are currently 28,500 U.S. troops in South Korea.

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Kim, believed to be 69, died of a heart attack at 8:30 a.m. local time Saturday, a weeping TV announcer dressed all in black told the nation.

He died "from a great mental and physical strain ... on [a] train during a field guidance tour," Yonhap reported, citing the North Korean Central News Agency.

The isolated leader's death has renewed fears that North Korea and its neighboring countries will face a dangerous period of instability under the rule of Kim's successor, his youngest son, Kim Jong Eun.

After the dictator's death was announced, US President Barack Obama spoke by telephone to South Korean president Lee Myung-bak and reaffirmed his commitment to close national security coordination, the White House said in a statement.

"The president reaffirmed the United States' strong commitment to the stability of the Korean peninsula and the security of our close ally, the Republic of Korea," it said, in reference to South Korea. "The two leaders agreed to stay in close touch as the situation develops and agreed they would direct their national security teams to continue close coordination."

A US official said, "South Korea's concern is warranted, frankly, because an insecure North Korea could well be an even more dangerous North Korea."

South Korea's Defense Acquisition Program Administration said Monday that the South had also completed the deployment of its indigenous guided missile, Yonhap reported.

Cross-border tensions have been high since Seoul accused Pyongyang of torpedoing a warship off the east coast of the peninsula with the loss of 46 lives in March 2010. The North denied the charge but went on to shell the Yeonpyeong border island, briefly sparking fears of war.

Since then, Seoul has staged a series of military exercises either alone or jointly with its ally the US in a show of force, while Pyongyang routinely test fires short-range missiles either as part of a training exercise or as a reaction to political developments.

NewsCore and Fox News' Jennifer Griffin contributed to this report.