U.S. President Barack Obama visited the demilitarized zone dividing the two Koreas Sunday.

The president, standing behind thick, bulletproof glass peered across the border into North Korea with the help of powerful binoculars.

Mr. Obama also met with American troops guarding the DMZ and told them they are a long line of soldiers who have enabled South Korea to prosper. He told the soldiers that South Korean President Lee Myung-bak had once confided he was able to rise from poverty as a child, to a successful career thanks in large part to America's military aid and support.

President Obama visited the DMZ hours after arriving in South Korea, flying into at a U.S. air base south of Seoul. He is in South Korea for this week's global summit on nuclear security. He also plans various bilateral meetings with world leaders on the sidelines of the summit.

The gathering comes days after North Korea announced plans to launch what it calls an observation satellite on a long-range rocket next month. The North's nuclear ambitions, along with those of Iran and other countries will be the focus of the leaders of more than 50 nations at the summit, which begins Monday.

The U.N., U.S., European Union, Russia and Japan have warned North Korea that the plan is in violation with U.N. resolutions, and urged Pyongyang to abandon the plan. Even North Korea's ally China has expressed concern that such a rocket launch would undermine stability in the region.

The United States has said the launch would cancel an agreement with North Korea to send it a large shipment of U.S. food aid in exchange for halting its nuclear and long-range missile programs.

North Korea announced Saturday it would hold an annual parliamentary session April 13 amid preparations for the rocket launch.

Deputy U.S. National Security Adviser Ben Rhodes said last week that the main points of the DMZ visit are to show support for the more than 28,000 U.S. troops serving in Korea and to stress the U.S. security alliance with South Korea.

The DMZ is considered one of the most dangerous places on earth, with heavily-armed North and South Korean forces aligned against one another. The two have remained in a formal state of war since an armistice ended combat in the Korean War in 1953.

The White House says while in South Korea, Mr. Obama will hold various bilateral meetings, including talks with Chinese President Hu Jintao. Mr. Obama also plans to meet with the leaders of Kazakhstan, Russia, South Korea and Turkey on the sidelines of the summit. He is also expected to meet with Pakistani Prime Minister Yousuf Raza Gilani to review efforts to support an Afghan-led reconciliation process with the Taliban.