More than 100 South Koreans traveled by road to North Korea Wednesday, marking the opening of a new overland route across the world's most heavily fortified border. The trip comes amid growing worries over North Korea's nuclear weapons program.

A convoy of buses carrying South Korean tourism officials and their guests snaked across the border between the two Koreas Wednesday despite the nuclear standoff on the peninsula.

Troops from both countries and the United States watched the vehicles as they crossed the Demilitarized Zone, a four kilometer-wide no man's land that divides the South from the North. The destination was the North's Mount Kumgang resort.

The South has been subsidizing tourist trips by sea to the resort for more than three years.

Wednesday's trip was a test run for the first overland tourist excursions to the North in half a century. The official tours, run by South Korea's Hyundai conglomerate, are scheduled to start later this month. There are no plans to open the road to ordinary motorists.

"The road will save a lot of time and money for the cost of the journey, " explains Tim Savage, a researcher on North Korea at Kyongnam University in Seoul. "So it will allow Hyundai to cut the price of its tours and hopefully that will generate a lot more revenue. They have lost a lot of money thus far on the Kumgang Mountain tour. There has been sort of a sense from the pro-engagement people in the government and the Hyundai Corporation that is it important to normalize these exchanges and reduce tensions over the long term."

The tours are one of a series of economic and humanitarian projects promoting peace between the two Koreas, which remain technically at war because their conflict ended in 1953 in an armed truce. South Korean President Kim Dae-jung and his Northern counterpart, Kim Jong Il, agreed on the projects at their historic summit in 2000.

Despite this sign of progress in North-South relations, North Korea's nuclear development program remains on top of both countries' political agendas. South Korean President Kim Dae-jung on Wednesday urged North Korea to drop its nuclear ambitions, repeating his view that the nuclear standoff must be resolved peacefully through dialogue.

But North Korea said Wednesday it would put in place "stronger self-defensive measures" following U.S. proposals to increase its forces in the Pacific. Pyongyang's official Korean Central News Agency accused Washington of trying "to crush the North to death."

U.S. defense officials are considering sending reinforcements to the western Pacific to deter any North Korean aggression in case of a U.S. led war with Iraq. The United States has about 37,000 troops in South Korea, intended to help defend the country from attack by the North.

The North's state run media also said the country would work toward a peaceful and fair resolution to the impasse over its nuclear ambitions. That follows comments from U.S. Deputy Secretary of State Richard Armitage, who said Tuesday in Washington that the Bush administration is prepared to hold direct talks with the North.

The crisis began in October, when the United States said North Korea admitted having a covert nuclear weapons program, in violation of several international treaties. It has since unsealed nuclear facilities and pulled out of the Nuclear Non-Proliferation Treaty.