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Kim Kwang Hyon, Associated Press
Kwak Chol Hui, deputy director of North Korea's National Defense Commission, attends a news conference in Pyongyang on Saturday March 3, 2012 to discuss joint U.S.-South Korean war games which North Korea says threatens regional peace and stability. South Korea and the U.S. said the war games taking place in the South are routine exercises. Pyongyang sees the drills as a major affront coming two months after the death of leader Kim Jong Il.

SEOUL, South Korea — North Korean leader Kim Jong Un ordered troops along the heavily armed border with rival South Korea to be on high alert during a visit to the Demilitarized Zone, state media reported Sunday.

Kim's visit to Panmunjom village, his first reported trip there since the December death of his father, Kim Jong Il, comes amid escalating militaristic rhetoric aimed at U.S. ally South Korea just days after Washington and Pyongyang agreed to a nuclear deal after years of deadlock.

Recent North Korean threats, including vows of a "sacred war" against Seoul over U.S.-South Korean military drills, appear to be aimed at a domestic audience, analysts say, and could be an effort to bolster Kim Jong Un's credentials as a military leader after showing off his diplomatic skills on the U.S. nuclear deal.

Still, the rhetoric keeps the region on edge and complicates diplomatic efforts to settle the standoff over North Korea's nuclear weapons program. North Korea has acted on its threats in the past. Violence in 2010 killed 50 South Koreans and led to fears of a broader conflict.

On Sunday, tens of thousands of North Koreans rallied in Pyongyang, vowing to topple South Korean President Lee Myung-bak, who ended a no-strings-attached aid policy to the North when he took power in 2008, instead linking assistance to nuclear disarmament.

In rhetoric typical from the North, military chief Ri Yong Ho warned in a speech at Pyongyang's main Kim Il Sung Square that the North Korean army would "sweep out" the South Korean traitors using their guns.

A crowd of soldiers and citizens later paraded through the plaza, pumping their fists and chanting, "Let's kill Lee Myung-bak by tearing him to pieces."

The threats are aimed internally as Kim Jong Un bolsters his power among the elite and military as the third generation of his family to lead the country, said Jeung Young-tae, an analyst with the Korea Institute for National Unification in Seoul.

"It's something that Kim Jong Un must do as the successor," Jeung said Sunday. "The North did a similar thing when Kim Jong Il appeared as the new leader" in 1994 following the death of his father, North Korea founder Kim Il Sung.

North Korea accuses the U.S. and South Korea of holding the joint military drills as preparation for a northward invasion. The allies' military exercises began last week and are scheduled to end in April.

During his Panmunjom visit, Kim Jong Un told troops to "maintain the maximum alertness as they are standing in confrontation with the enemies at all times," according to the official Korean Central News Agency.

On Saturday, a spokesman for North Korea's National Defense Commission told a news conference that the United States must halt the joint military drills if it is serious about peace on the Korean peninsula.

North Korea calls the U.S.-South Korean war games a threat to peace at a time when U.S. and North Korean officials are holding talks aimed at improving relations.

The U.S. and North Korea announced last week that Washington had agreed to provide 240,000 metric tons of food aid in exchange for a freeze of North Korea's nuclear activities. A U.S. envoy is scheduled to meet with North Korean officials in Beijing on Wednesday to discuss the distribution of food.

The deal is seen as a first step toward resuming six-nation nuclear disarmament-for-aid talks suspended in 2009, and a tentative move toward improving the tense relationship between the wartime foes. The six-nation talks involve the two Koreas, the U.S., China, Russia and Japan.

"Talks and military exercises are contradictory," Maj. Gen. Kwak Chol Hui, deputy director of the National Defense Commission's Policy Department, told the news conference Saturday in response to a question from The Associated Press. "If the U.S. really stands for peace and stability on the Korean peninsula, it should stop the aggression-oriented war rehearsal and revise the hostile policy toward the DPRK."

DPRK stands for North Korea's formal name, the Democratic People's Republic of Korea.

The United States and South Korea say the military drills are routine annual exercises. The U.S. keeps more than 28,000 troops in South Korea as a legacy of the three-year Korean War of the 1950s, which ended in a truce, not a peace treaty.

North Korea considers the drills an additional affront because they are being staged during the semiofficial 100-day mourning period following late leader Kim Jong Il's Dec. 17 death.

The Supreme Command of the Korean People's Army threatened "a merciless sacred war" against South Korea in a statement provided to the AP on Friday.

Across Pyongyang, vans mounted with speakers drove through the streets Saturday broadcasting the statement denouncing South Korea. State media reported that 1.7 million young North Koreans signed up for military service in a 24-hour period and that hundreds of thousands signed petitions calling for revenge. The figures could not be confirmed independently.

Associated Press writers Kim Kwang Hyon and Pak Won Il contributed to this report from Pyongyang, North Korea.