SEOUL, South Korea >> North Korean leader Kim Jong Un visited the heavily armed border with rival South Korea and ordered troops to be on high alert, state media reported Sunday, just days after Washington and Pyongyang agreed to a nuclear deal after years of deadlock.

Kim’s visit to Panmunjom village in the Demilitarized Zone, 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.

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. Washington has said that better inter-Korean ties are crucial for diplomacy to succeed. North Korea has also acted on its threats in the past. Fifty South Koreans died in violence blamed on North Korea in 2010, leading 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. The city’s main Kim Il Sung Square was packed with soldiers dressed in olive green uniforms and citizens who stood at attention as speakers criticized Lee’s government. Huge propaganda placards and portraits of Kim Il Sung and Kim Jong Il towered above the crowd.

In rhetoric typical of the North, military chief Ri Yong Ho warned in a speech that the North Korean army would "sweep out" the South Korean traitors using their guns, according to footage from North Korea’s state TV.

Soldiers and citizens later paraded in rows through the plaza, carrying fluttering red flags, 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. "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, he said.

North Korea accuses the United States and South Korea of holding the joint military drills as preparation for a northward invasion. The allies say the military exercises, which began last week and are scheduled to end in late April, are routine and defensive in nature.

Pyongyang is also angry about a South Korean military unit near Seoul recently posting threatening slogans beneath portraits of Kim Jong Un and his father.

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.

State TV aired photos of Kim, dressed in a dark overcoat, shaking hands with a helmeted soldier and giving rifles and machine guns as souvenirs to troops.

Panmunjom is a cluster of huts inside the 154-mile (248-kilometer) -long DMZ, which is jointly overseen by the U.S.-led U.N. Command and North Korea in an arrangement established in 1953 to supervise the cease-fire that ended the three-year Korean War. About 28,500 American troops are still stationed in South Korea.

Panmunjom has drawn other high-profile visitors in times of tension.

U.S. Secretary of State Hillary Rodham Clinton and then Defense Secretary Robert Gates traveled there in July 2010, four months after a warship sinking blamed on Pyongyang killed 46 South Korean sailors. North Korea has denied involvement. In 2002, then President George W. Bush visited Panmunjom a few weeks after he condemned North Korea as part of an "axis of evil."

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.

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

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.

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