Jeon Heon-Kyun/Pool / EPA

South Korean soldiers stand guard at the Military Demarcation Line in the Demilitarized Zone that separates the two Koreas since the Korean War, in the border village Panmunjom in Gyeonggi-do, South Korea.

President Barack Obama, seeking to increase pressure on North Korea to abandon its atomic weapons, will visit the Demilitarized Zone 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.

Ben Rhodes, deputy national security adviser, said the trip has two purposes for Obama.

"The first is the focus he has put on nuclear security along with non-proliferation since the beginning of his time in office," Rhodes said. "And the second is, of course, our increased focus on the Asia Pacific as a region of great importance to the United States."

Obama will meet with U.S. troops at the DMZ during the trip, his third to South Korea in three years, White House officials said.

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.

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.

This article includes reporting by Reuters.

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The Iranian government has blocked attempts to investigate its alleged atomic weapons work, the U.N.’s nuclear watchdog agency said Wednesday.

The U.N. International Atomic Energy Agency, or IAEA, expressed disappointment over a lack of progress during two days of talks in Tehran over Iran's disputed nuclear program and said its request to visit a military site had not been granted.

In the second such visit in less than a month, a senior team from the IAEA had traveled to Tehran to press Iranian officials to start addressing mounting concerns that the country may be seeking to develop atomic arms.

"During both the first and second round of discussions, the agency team requested access to the military site at Parchin. Iran did not grant permission for this visit to take place," the Vienna-based IAEA said in a statement after the talks Monday and Tuesday talks in the Iranian capital.

The statement was released early Wednesday, after the IAEA team left on a return flight to Vienna. The unusual timing — shortly after midnight in Europe — reflected the urgency the IAEA attached to the communique.

NYT: Mother visits American sentenced to death in Iran

Iran denies any interest in possessing nuclear weapons and says its atomic program is for peaceful purposes.

In the latest in a war of words between the West and Iran, an Iranian general warned Tuesday that the nation will pre-emptively strike anyone who threatens it.

The statement by Gen. Mohammed Hejazi continues the defiant tone Tehran has taken in its confrontation with Western countries that claim it is developing nuclear weapons.

"We do not wait for enemies to take action against us," said Hejazi, according to the semiofficial Fars news agency. "We will use all our means to protect our national interests."

Hejazi heads the military's logistical wing.

The U.S. and Israel have not ruled out strikes against Iranian nuclear facilities.

Iran also said Tuesday that a visiting U.N. team did not plan to inspect the country's nuclear facilities and would only hold talks with officials in Tehran.

The statement cast doubt on how well U.N. inspectors can gauge whether Iran is moving ahead with its suspected pursuit of nuclear weapons.

Iran threatens pre-emptive action amid nuclear tensions

The visit by the International Atomic Energy Agency team, which started Monday, is the second in less than a month.
Foreign Ministry spokesman Ramin Mehmanparast said the visiting IAEA team was made up of experts, not inspectors. He told reporters that the IAEA team was holding discussions Tuesday in Tehran to prepare for future cooperation between Iran and the U.N. watchdog. He said this cooperation is at its "best" level.

"The (title) of the members of the visiting delegation is not 'inspectors.' This is an expert delegation. The purpose of visit is not inspection," said Mehmanparast. "The aim is to negotiate about cooperation between Iran and the agency and to set a framework for a continuation of the talks."

Visits to Iranian nuclear sites were not part of the IAEA visit three weeks ago.

The latest IAEA trip came as Iran carried out air defense war games to practice protecting nuclear and other sensitive sites.

The official news agency IRNA said Monday that the four-day air defense war games — dubbed "Sarallah," or "God's Revenge" — were taking place in the south of the country and involved anti-aircraft batteries, radar and warplanes. The drill was to be held over 73,000 square miles near the port of Bushehr, the site of Iran's lone nuclear power plant.

Iran has held multiple air, land and sea maneuvers in recent months as the tensions increased.

The military maneuvers are viewed as a message to the West that Iran is prepared to defend itself against hostile measures and to retaliate — including warnings that it could cut the strategic Strait of Hormuz waterway off its southern coast with its naval forces.
Tehran is also under heavy economic pressure. Last month, the European Union imposed sanctions on Iran's fuel exports and froze its central bank assets. An oil embargo is set to begin in July.

Iranian officials said the country should respond by cutting off EU states early, before they can line up alternative buyers. Over the weekend, Tehran announced that it was pre-emptively cutting off exports to France and Britain.

 Reuters and The Associated Press contributed to this report.

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