U.S. keeps close watch on North Korea as threats continue

Kim Jong Un
A photo released by the Korean Central News Agency (KCNA) shows North Korean leader Kim Jong Un giving a speech during a plenary meeting of the central committee of the ruling Workers' Party in Pyongyang, North Korea, March 31, 2013.

(CBS News) -- The U.S. Navy is moving radar and anti-missile systems towards North Korea -- part of a military build-up after belligerent threats from North Korea's new dictator.

Kim Jong Un
North Korean leader Kim Jong Un, March 31, 2013. AP Photo/KCNA via KNS

Thirty-year-old Kim Jong Un took over from his late father just over a year ago and he is not the first North Korean dictator to threaten war with South Korea and its American allies.

But this time is different. South Korea's new President Park Geun-hye is dealing with a new political reality.

Retired general Walter Sharp says the South Korean people have stated they're not going to stand for this anymore.

Sharp, former commander of U.S. forces in Korea, says another incident like the 2010 shelling of a South Korean island would trigger not just a tit-for-tat retaliation but a combined attack by U.S. and South Korean forces.

South Korean President, Park Geun-hye. CBS News

"Things have changed since November 2010 and if he does another attack like that, the response is going to be swift and it's going to be strong," said Sharp.

Sharp began the retaliation planning after the 2010 shelling in which the north fired about 170 rounds, killing four South Koreans.

The Seoul Government was criticized for a weak response and the U.S. and South Korea began preparing a much tougher retaliation for the next time.

"What should we do to be able take something of value to Kim Jong Un and hold that at risk?" said Sharp.

Retired United States general Walter Sharp. CBS News

"There are things that North Korea has, in the past, really valued. Where they have put their money into their military forces? They put it into nuclear facilities. They've put it into ballistic missiles."

For now, the U.S. is making a point of showing off all the firepower it could bring to bear. Everything from F-22 stealth fighters to B-2 stealth bombers, flying into and over South Korea.

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Ground-Based Midcourse Defense (GMD) sea-based radar platform arrives in Pearl Harbor aboard Heavy lift vessel Blue Marlin in January, 2006.
The U.S. Navy is moving radar system - like this Ground-Based Midcourse Defense (GMD) sea-based platform - towards North Korea. U.S. Navy photo/ournalist 2nd Class Ryan C. McGinley
  • David Martin

    David Martin is CBS News' National Security Correspondent.