About 100,000 flag-waving South Koreans marched with candles in downtown Seoul in the biggest protest yet over the impending resumption of U.S. beef imports Tuesday while police guarded the presidential office with a giant barricade.

Shouting, "Renegotiate!", the demonstrators took part in Tuesday's candlelit protests. Some 20,000 riot police were being mobilized. The South Korea's largest candlelight rally was held here to pressure the Lee Myung-bak administration to renegotiate an agreement to open South Korea's market to U.S. beef with almost no restrictions.

Protesters rally on a street leading to the U.S. embassy and the presidential Blue House in central Seoul June 10, 2008. (Xinhua/Reuters Photo)

The entire cabinet earlier offered to quit to take responsibility for weeks of turmoil over the deal, which opponents say exposes South Koreans to the risk of mad cow disease.

A presidential spokesman said no decision had been made yet about ministerial changes and the current cabinet would stay in office for the time.

Police went on the highest alert, erecting a giant barricade at the protest venue. The 5.5-meter high barricade, built with dozens of 4-ton containers, completely blocked the Gwanghwamun street adjacent to the U.S. Embassy, just about one kilometer away from the presidential office of Cheong Wa Dae.

Police put the crowd at 100,000, while organizers claimed there were 700,000.

"By this, President Lee Myung-bak is saying that he doesn't want to talk about it anymore," Yong Sang-soon, a demonstrator who came after work, said. Agriculture Minister Chung Woon-chun appeared at the protest venue, saying "I came to apologize directly to the public." But his move was thwarted by angry protesters.

On the national level, organizers expected up to one million people at the candlelight vigils from the southern resort island of Jeju to the second-largest city of Busan.

Police place South Korean flags on cargo containers that hold sand to form a barricade to block a planned protest march on a street leading to the U.S. embassy and the presidential Blue House in central Seoul June 10, 2008.(Xinhua/Reuters Photo)

Unionized workers walked off their jobs to protest the U.S. beef deal. The Korean Confederation of Trade Unions, the more radical of the country's two umbrella labor unions, warned it will launch indefinite walkout next week. Resentment in the labor sector particularly rose following the death on Monday of a blue-collar worker who immolated himself during a beef protest about two weeks ago.

Seoul agreed in April to allow imports of U.S. beef from all ages of cattle, banning only specified risk materials -- such as tongues, brains, part of the intestines and vertebrae marrow that are known to have the greatest risk of transmitting mad cow disease to humans -- from cattle older than 30 months.

President Lee has repeatedly stated that South Korea will only import U.S. beef from cattle younger than 30 months old. He asked for Washington's cooperation in his first-ever telephone talk with U.S. President George W. Bush over the weekend.

Critics say the beef pact cannot protect South Koreans from the disease. Civic groups have suggested that Seoul impose stricter guidelines to ban meat from cattle older than 20 months, as Japan does. Younger cattle are generally less prone to contracting the brain-wasting illness.

U.S. legislators have warned they will not ratify the free trade agreement unless Seoul first opens its beef market.

Editor: Yan