SEOUL — 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.
Mr. 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 also has 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 and citizens who stood at attention as speakers criticized Mr. Lee's government. 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," Mr. 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.
Panmunjom is a cluster of huts inside the 154-mile-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 U.S. troops are still stationed in South Korea.