By Alister Bull and Matt Spetalnick
WASHINGTON (Reuters) - President Barack Obama, seeking to increase pressure on North Korea to abandon its atomic weapons, will visit the Demilitarized Zone (DMZ) on South Korea's tense border on Sunday before a nuclear security summit in Seoul.
Obama's visit to the border will be a strong show of support for South Korea, the White House said on Tuesday, sending a message to the North as Washington builds an international effort to get stalled nuclear disarmament talks back on track.
North Korea will not attend the summit, where Obama will meet with Chinese President Hu Jintao and urge him to use Beijing's long-standing influence with Pyongyang, where leadership has recently passed to Kim Jong-un.
"We certainly hope and recommend that China bring all the instruments of power to bear to influence the decision-making in North Korea," said Daniel Russel, White House National Security Council senior director for Asia.
Secretive North Korea has twice tested a nuclear device, and the United States says its long-range ballistic missile program is progressing quickly.
While experts doubt North Korea has the ability to miniaturize an atomic bomb to place atop a warhead, last year Washington warned that the American mainland could come under threat from North Korean missiles within five years.
ROCKET LAUNCH PLAN
Last month, North Korea reached an agreement with Washington to suspend nuclear tests, long-range missile launches and uranium enrichment as part of a deal to restart food aid, but then announced it would launch a rocket carrying a satellite to mark the centenary of founder Kim Il-sung's birth next month.
The United States has said this plan could violate the nuclear moratorium deal and scuttle the resumption of food aid.
Obama's visit to the DMZ, which splits the peninsular that was divided by the 1950-1953 Korean war, was cast by the White House as a chance for him to thank some of the more that 20,000 U.S. troops still stationed in South Korea.
Beijing is the closest thing North Korea has to an ally but has also voiced concern about the planned rocket launch, which has raised tensions ahead of the March 26-27 summit, dedicated to reducing the threat of nuclear terrorism.
North Korea will loom large, as well as Iran's nuclear program, which has spurred worries about the possibility of fresh military conflict in the oil-rich Middle East.
"North Korea will be the odd man out," said Russel in a conference call previewing the trip.
"The nations that will gather in Seoul will assemble in a modern prosperous city, in an open and democratic society ... The choices that the North Korean leaders have made have taken the people of North Korea into isolation and poverty."
Obama will also meet Russian President Dmitry Medvedev and South Korean President Lee Myung-bak on the sidelines of the summit to discuss what can be done to discourage the missile launch and Pyongyang's nuclear program.
Obama will also discuss with Hu and Medvedev the latest world power efforts to tackle Iran over its nuclear program, which the West says is aimed at building an atomic bomb but Tehran insists is for peaceful power generation.
"We are committed to pursuing a diplomatic path that allows the Iranians to make the right decision," said White House National Security Council spokesman Ben Rhodes.
Washington has urged Israel to hold off from attacking Iran's nuclear sites to give more time for international sanctions and diplomacy to work, but Obama has also said that he would not allow Tehran to acquire a nuclear weapon.
(Reporting By Matt Spetalnick; Editing by David Brunnstrom)