South Korea (search) said Tuesday a U.S. plan to cut a third of its 37,000 troops from the South has not been finalized, but it pledged to beef up its own forces amid concerns of a security vacuum along the Cold War's last frontier.

The proposal to pull out the troops by the end of next year would force South Korea to shoulder more responsibility for defending itself from possible North Korean military aggression.

But the plan spurred concern that the North could view a U.S. troop withdrawal as a sign of weakness as the communist country wrangles with its neighbors and Washington over its nuclear weapons program.

South Korean Defense Minister Cho Young-kil tried to quell security concerns, as South Korea and the United States opened a second day of talks on a separate plan to move American troops away from the tense Demilitarized Zone (search) that has divided the two Koreas since the end of the 1950-53 Korean War.

"We have to have further negotiations," Cho said of the U.S. withdrawal plan. "It has not yet been decided."

"Concerning concerns about a security vacuum, we will take measures to ensure that the U.S.-South Korea deterrent capability is not diminished, and we will make efforts to strengthen our deterrent capabilities."

President Roh Moo-hyun (search) has said in the past that South Korea must chip in more for its own defense, but some in the South voiced concern about the size and quick timetable for the proposed U.S. withdrawal.

The U.S. plan calls for withdrawing 12,500 of the 37,000 U.S. troops stationed in South Korea over 2004 and 2005, according to a statement released Monday by the U.S. military in Seoul. It would be the first major U.S. troop cut in South Korea since the early 1990s, when the allies coordinated the removal of 7,000 soldiers.

The United States has stationed troops in South Korea since the end of the Korean War — partly as a deterrent against North Korea and partly as a counterbalance to other regional powers. The Korean War ended in a cease-fire, not a peace treaty, and the two sides are technically still at war.

South Korea's 650,000-member military is a modern, well-equipped force that routinely conducts joint training with U.S. counterparts. Most of the combat-ready troops are concentrated close to the border or around Seoul.

Cho did not give any details Tuesday about how the South might bolster its military deterrent.

North Korea has a formidable arsenal of missiles and more than 1 million soldiers, but it is said to have fuel shortages and lack spare parts for its decrepit military hardware, some of which dates to the 1950s.

Washington has said it will spend $11 billion over the next five years to upgrade its military in the theater as part of a global overhaul to focus on firepower and improved flexibility of troops to rush to global hotspots.

"We are realigning our force posture to respond more effectively to the threats of the 21st century," U.S. State Department spokesman Adam Ereli said Monday in Washington.

News of the planned troop withdrawal coincided with talks between the two allies on the U.S. plan to reposition most of its forces currently stationed near the North Korean border to points south of the South Korean capital, Seoul.

That proposal also would transfer about 7,000 U.S. forces and their families from the sprawling Yongsan Base in downtown Seoul to an expanded facility south of the capital by 2006.

The two-day Future of the Alliance talks were scheduled to end Tuesday.