US President Barack Obama will come face-to-face with the chill legacy of the Cold War on Sunday by visiting the tense and fortified border zone between the two Koreas.

Obama wants to pay tribute to some of the 28,500 US soldiers serving in South Korea, and to honor the strength of their host nation, a key ally in Asia, a region to which he has reoriented American foreign policy.

The president will also Sunday meet South Korean President Lee Myung-Bak to prepare a 53-nation nuclear security summit in Seoul, a day before holding more key talks with China's President Hu Jintao, officials said.

He will also Monday hold his last meeting as an equal with outgoing Russian President Dmitry Medvedev with whom he masterminded a reset of US ties with the Kremlin, and will see leaders of Turkey and Kazakhstan.

"The president will visit the demilitarized zone which will be an important opportunity to thank some of the American troops for serving on the Korean peninsula," said Ben Rhodes, a senior Obama aide.

The trip will "also underscore the strength of the Republic of Korea and our strong commitment to their security," said Rhodes, deputy national security advisor for strategic communications.

Officials did not say whether Obama was intending to send a message to Stalinist North Korea with his visit to the DMZ, but said he would renew his call for Pyongyang to live up to international nuclear standards.

The visit may though come to be seen as carrying a symbolic challenge to North Korea's new leader Kim Jong-Un, who succeeded his late father Kim Jong-Il, who had confounded the United States and its allies for years.

The DMZ is known as the world's last Cold War frontier, and separates the thriving capitalist south from isolated, impoverished communist North Korea which has defied the world with its nuclear drive.

Splitting the two Koreas since the 1950-53 war, the four-kilometer-wide (2.5 miles) DMZ features guard posts manned by rival armies and barbed wire, and roads bisecting minefields.

Former US president Bill Clinton called the DMZ the "scariest place on earth" after inspecting a chilling landmark also visited by his successor George W. Bush.

Cross-border tension has been high since Seoul accused Pyongyang of torpedoing one of its warships with the loss of 46 lives in March 2010.

The North angrily denied involvement but went on to shell a border island and kill four South Koreans in November the same year.

Obama will visit South Korea at a time of conflicting signals and diplomatic brinkmanship by Pyongyang.

Pyongyang has invited UN inspectors to monitor a nuclear freeze deal with the United States, but has also announced it plans a satellite launch which Washington sees as a bid to test new long-range missile technology.

Obama's trip to South Korea will again underscore the decision he took to weight foreign policy more towards Asia, a dynamic region he sees as crucial to future US prosperity and security.

After visiting the DMZ on Sunday, Obama will hold talks, a press conference and have dinner with Lee, who has emerged as one of his closest friends on the world stage.

Officials said the two men would discuss the nuclear security summit, and economic ties between their nations as a free trade pact goes into force.

On Monday, March 26, Obama will give a speech at Hankuk University of Foreign Studies in Seoul, where he will talk about the rising role of South Korea as both a regional and global player.

Obama will also use the appearance to lay out his goals for the nuclear security summit, which follows up on the inaugural meeting hosted by the US leader in Washington two years ago.

The purpose of the initiative was to take aim at what the White House sees as the greatest threat to US security -- that terrorists could acquire unsecured nuclear material or get hold of a nuclear weapon.

US officials say the Seoul summit will highlight the achievements made in Washington -- saying 80 percent of commitments secured at that meeting on securing loose nuclear materials have been honored.