President Obama Sunday visited the highly fortified Demilitarized Zone (DMZ) which separates South Korea and North Korea.

Obama traveled to a US military base located at the edge of the 2.5 mile wide DMZ and greeted the soldiers there, as a symbolic reassurance of its support to South Korea.

You guys are at freedom's frontier, Obama told about 50 troops crammed into the Camp Bonifas mess at the army centre, Reuters reported.

The contrast between South Korea and North Korea could not be clearer, could not be starker, both in terms of freedom and in terms of prosperity, he added.

He later traveled to an observation post in the heavily patrolled border and spent 10 minutes talking to soldiers. He peered into the North Korean boundary with the help of binoculars and pointed something at the distance, Reuters report said.

Obama's visit to the DMZ amid a nuclear standoff with North Korea gains significance as North Korea is stubbornly perusing its plan to launch a satellite using a ballistic missile technology, despite warnings from America against it.

With the visit, Washington aims at showcasing the strong US-South Korea bonding while sending a stern message to North Korea against its clandestine nuclear program. The visit also is seen as a way to boost Obama's image as a tough commander-in-chief in America ahead of the November presidential elections.

Obama is the fourth American President to visit the Demilitarized Zone. Other Presidents who visited the highly guarded border are Ronald Reagan, Bill Clinton and George W. Bush. Nearly 30,000 soldiers are still deployed here.

Obama is in South Korea to participate in a nuclear security summit to discuss nuclear safety and nuclear terrorism, hosted by Seoul. More than 50 world leaders would participate in the summit and Obama is scheduled have several bilateral meetings during the two-day summit.

Though North Korea is not in the official agenda of the summit, yet it is expected to be discussed in bilateral meetings between Obama and the heads of other world powers.

North Korea Mourns: While the President Obama visited the DMZ and peered into the North Korean territory Sunday, North Korea was observing the 100th after the death of its former leader Kim Jong-il who died in December. Thousands of people participated in a ceremony held in Kim Il-sung Square in central Pyongyang to mark the end of 100-day mourning period of the leader, a Reuters report said.