PANMUNJOM, South Korea - President Obama warned North Korea on Sunday that its threats and provocations would only deepen its international isolation and jeopardize the resumption of food aid from the United States, and he called on the North to scrap its plans to launch a satellite next month.
Seoul warned Monday that it might shoot down the North Korean long-range missile carrying the satellite if it strays into South Korean territory.
Squinting through binoculars from an observation post at the demilitarized zone between North and South Korea, Obama got a firsthand look at North Korea, which had briefly tantalized the United States just weeks ago by raising the possibility of ending the standoff over its nuclear program with a new leader in place, only to resume its usual defiant stance with the recent satellite announcement.
“They need to understand that bad behavior will not be rewarded,’’ Obama said, referring to the North Koreans at a news conference with South Korea’s president, Lee Myung Bak, who is hosting a nuclear security summit meeting that will include Obama and 50 other world leaders.
Lee also demanded that North Korea repeal the decision to launch the satellite, which is to be mounted on a long-range missile.
Both men said it would breach North Korea’s obligations, since missile launchings are barred by United Nations sanctions.
Despite the international condemnation, North Korea appears determined to press ahead with the satellite launch next month. On Sunday, the South Korean military said that North Korea had moved the main body of its Unha-3 rocket to the newly built launching station in Dongchang-ri, a village in northwestern North Korea.
“We are studying measures such as tracking and shooting down [parts] of a North Korean missile in case they stray out of their normal trajectory’’ and violate South Korean territory, said Yoon Won Shik, a vice spokesman at the Defense Ministry, on Monday.
“We cannot help viewing [the launch] as a very reckless, provocative act’’ that undermines peace on the Korean peninsula, he said.
Obama expressed frustration that China, as the main patron of the North Korean government, had not done more to curb the North’s provocative behavior. He said he would raise the issue in a meeting on Monday with the Chinese president, Hu Jintao.
“In the same way that North Korea needs to do something new if it wants to do right by its people,’’ Obama said, the Chinese must recognize that “the approach they’ve taken over the last several decades hasn’t led to a fundamental shift in North Korea’s behavior.’’
The president’s comments came on a day that brought home the intractable nature of the Korean conflict, as he tromped through guard posts and bunkers that date back six decades to the Korean War.
On the far side of the demilitarized zone, beyond the watchtowers and concertina wire that separates the two countries, a giant red-and-blue North Korean flag billowed at half staff, marking the 100th day since the death of Kim Jong Il, who led North Korea for 17 years.
It was Obama’s first visit to this heavily fortified border - Presidents George W. Bush, Bill Clinton, and Ronald Reagan also made the trek - and it seemed both an echo of the Cold War and a testament to new dangers in an age of nuclear proliferation.
The agenda for a nuclear security summit meeting, first held by Obama in 2010, is ostensibly about preventing nuclear materials from falling into the hands of terrorists.
But the motives and ambitions of states like North Korea and Iran are expected to dominate the discussions.
North Korea’s talk of launching a satellite upended a fragile diplomatic opening to Kim Jong Il’s son and successor, Kim Jong Un. Analysts say North Korea appears to be reverting to a familiar cycle of provocations, perhaps as its untested leader tries to consolidate his power.
Obama declined to speculate on the younger Kim, saying that “it’s not clear exactly who’s calling the shots’’ in North Korea.
Lee said he was disappointed because he had expected Kim to take a path different from his father’s.
During his visit to the demilitarized zone, Obama paid tribute to the soldiers who have patrolled this frontier, saying they made it possible for South Korea to grow into a thriving democracy with a free-market economy despite the constant threat of war from the North.
“You guys are at freedom’s frontier,’’ the president said to US troops in a dining hall at Camp Bonifas, an outpost of the UN command that oversees the zone. “The contrast between South Korea and North Korea could not be clearer, could not be starker,’’ he added, “both in terms of freedom but also in terms of prosperity.’’
At Observation Post Ouellette, one of the forward-most posts, Obama stepped into a bunker ringed by sandbags and camouflage burlap and shielded by a wall of two-inch-thick bulletproof glass. He was handed binoculars to survey the North Korea countryside.