The North says it has also been angered by joint US-South Korean military exercises.
But he said those movements were likely part of normal North Korean military exercises.
North Korea is angry over the possible sanctions and over upcoming U.S.-South Korean military drills.
The South Korean military raised its cyberattack readiness level Wednesday following the shutdown, the Defense Ministry said.
On Wednesday South Korean military jets staged mock 11 September raids in cities hosting World Cup games.
Admiral Mullen expressed support for Japanese participation in American and South Korean military exercises in the area.
ECONOMIST: North Korea��s belligerence stiffens the South��s spine
In 2009 North Korean authorities imposed a number of restrictions on the KIC after US-South Korean military drills.
First, act to discourage North Korean military ambitions -- and to deal with them if all else fails.
Beaming shortwave broadcasts into the North was the idea of Kim Sung-min, a former North Korean military propaganda writer.
It calls ongoing routine U.S.-South Korean military drills a threat to its existence.
Moreover, according to South Korean military officials, the North is on the verge of completing a "Super-EMP" nuclear warhead.
North Korea has threatened revenge for the sanctions and for ongoing routine U.S.-South Korean military drills it considers invasion preparation.
Some of the uncertainty lies in whether the North Korean military backs or tries to circumvent the younger Mr. Kim.
South Korea's Kospi dropped 0.3 percent to 1, 913.71 as tension brewed on the Korean Peninsula amid joint U.S.-South Korean military drills.
The new deal puts North Korean military facilities which were previously out of range within reach, as well as parts of China and Japan.
Mr. Kerry noted that Mr. Obama recently called off some additional U.S.-South Korean military exercises in an effort to lower tensions between Washington and Pyongyang.
In 2009 North Korean authorities briefly shut off entry to Kaesong industrial park after US-South Korean military drills, leaving hundreds of South Korean workers effectively trapped.
BBC: South Korea 'to withdraw staff' from Kaesong zone in North
Over the past two decades, Pyongyang has engaged in a series of provocative military actions that caused the deaths of South Korean military personnel and civilians.
South Korean media outlets have, in the past, accused North Korea of running an internet warfare unit aimed at hacking into US and South Korean military networks.
While filming, the crew were escorted by South Korean military officers, able to travel off the few roads only under the guidance of carefully drawn landmine maps.
CNN: Beyond the barbed wire: the accidental paradise of the DMZ
On his visit, Mr Chung said the South Korean military should be on "high alert to respond to any types of North Korean provocations", reports Yonhap news agency.
Defense officials acknowledged that North Korean military officers are particularly agitated by bomber flights because of memories of the destruction wrought from the air during the Korean War.
North Korea built its rocket almost entirely on its own, South Korean military experts said earlier this month after analyzing debris retrieved from the Yellow Sea in December.
Pyongyang also is incensed by joint U.S.-South Korean military drills taking place now south of the border, annual exercises that this year have included nuclear-capable bombers and fighter jets.
Those reports were confirmed in September 2010, when Mr. Kim appointed his son a four-star general in the North Korean military and to high-level posts in the ruling political party.
"We have said several times that the U.S.-South Korean military exercises are annual defensive exercises, " Kim Ho-nyun, spokesman for South Korea's Ministry of Unification, said at a news briefing Monday.
Communist Party School professor and North Korea expert Zhang Liangui tells China News Service that South Korea's bigger role in the routine US-South Korean military exercises may have provoked Pyongyang.
North Korea has been railing against joint U.S.-South Korean military exercises that are taking place in South Korea and has expressed anger over tightened U.N. sanctions for its February nuclear test.
The South Korean military said Thursday that its drills will take place in the seas southwest of Yeonpyeong Island between December 18 and 21, but bad weather forced a delay Saturday.
An "insider" also tells Global Times that the North Korean military previously detained three Chinese fishing boats sailing from northeast Dandong city this year and released two of them after collecting "fines".
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