The leaders of the United States and South Korea on Tuesday vowed no concessions to North Korea after months of high tension, saying the burden was on the communist state to end the crisis.

In a choreographed show of unity, US President Barack Obama and South Korean President Park Geun-Hye pledged to bolster defense cooperation and demanded that North Korea change course on its nuclear program before any new talks.

"The days when North Korea could create a crisis and elicit concessions -- those days are over," Obama told a White House news conference with Park, who took office in February as Northeast Asia's first woman leader.

Obama said that he and Park agreed in talks that "we are not going to reward provocative behavior" but kept the door open to eventual talks if North Korea's young leader Kim Jong-Un decides to embrace "a peaceful path."

"If Pyongyang thought its recent threats would drive a wedge between South Korea and the United States or somehow garner the North international respect, today is further evidence that North Korea has failed again," Obama said.

Tensions have appeared to subside since earlier this year when North Korea carried out its third atomic test and vowed to prepare for nuclear war against the United States, in remarks shrill even by Pyongyang's standards.

A US defense official said that North Korea has shifted two medium-range Musudan missiles away from a launch site, signaling that -- at least for the time being -- the regime has no imminent plans to test-fire them.

China, the primary supporter of North Korea, took one of its most concrete measures to date with the state-owned Bank of China closing the account of a North Korean bank accused by Washington of supporting the nuclear program.

Park, while not commenting directly on the bank action, credited China and Russia with enforcing sanctions on North Korea imposed by the UN Security Council.

"Such constructive efforts on the part of China and Russia are vital to sending a unified message to North Korea that their nuclear weapons will not stand," she said.

Park insisted that North Korea would feel consequences for a showdown that suspended work at Kaesong -- a joint industrial park once an emblem of inter-Korean cooperation -- and repeated her warning that the military would swiftly respond to any North Korean attack.

If North Korea harms citizens of the South, "we will make them pay," she said. "If North Korea engages in provocation, I will fully trust the judgment of our military."

Park's predecessor Lee Myung-Bak, while also a conservative, faced criticism at home for not preventing or responding to North Korean shelling of the border island of Yeonpyeong that killed four South Koreans in November 2010.

Lee, a self-made businessman who devoted himself to a smooth US-South Korea alliance at a time of rapid change in Asia, became one of Obama's closest foreign allies. Park was seen as looking to build some of the same personal chemistry.

Obama hailed Park, the daughter of slain dictator Park Chung-Hee, as "tough" but also "realistic" with "the wisdom to believe that conflict is not inevitable and is not preferable."

While North Korea dominated the summit, South Korea has avidly sought a bigger global role both in politics and culture -- as witnessed by the phenomenal success of superstar Psy.

Obama made a ready reference to Psy, joking that his daughters had taught him the now world-famous "Gangnam Style" moves.

In a sea change from anti-US sentiment in South Korea a decade ago, Park invited US veterans to a gala dinner at the National Portrait Gallery to mark the 60th anniversary of the armistice that ended the Korean War.

She met at the museum with Defense Secretary Chuck Hagel who, according to a spokesman, assured her that "the full range of alliance capabilities" remained ready to respond to North Korea.

Park on Wednesday will address a joint meeting of Congress. Accompanied by leaders of major South Korean businesses, she will also visit the US Chamber of Commerce to mark one year after a free trade deal entered force.