Security staff and aides from the ruling party stood guard outside the room to keep opposition lawmakers away after the committee's GNP-affiliated chairman invoked his right to use force to "keep order" in parliamentary proceedings.
Scuffles broke out as dozens of opposition members and their aides attempted to push their way into the office. TV footage showed people from both sides shoving, pushing and shouting in a crowded hall at the National Assembly building amid a barrage of flashing cameras.
Opponents later used a sledgehammer and other construction tools to tear open the room's wooden doors, only to find barricades of furniture set up inside as a second line of defense.
Cable news channel YTN reported that an electric saw was used to open the door. YTN footage showed security guards spraying fire extinguishers at those trying to force their way inside and one man with blood trickling down his face.
The opposition attempt failed, and 10 GNP legislators introduced the bill to the committee.
"This is a clear violation of law," the main opposition Democratic Party said in a statement, accusing the GNP of illegally occupying the parliamentary chamber and unilaterally introducing the bill. "This is a declaration of war against the opposition and the people."
Clashes between lawmakers are not unusual in the National Assembly. Such violence has long been cited as one of the worst ills of South Korean politics.
South Korea and the United States signed the accord that calls for slashing tariffs and other barriers to trade in April last year after 10 months of tough negotiations, though neither side's legislature has yet ratified it - the key step needed for it to take effect.
The pact is the largest for the U.S. since the North American Free Trade Agreement with Canada and Mexico and the biggest ever for South Korea. NAFTA, signed in 1993, took effect the following year.
Proponents in both countries say it would not only expand trade but further cement ties between Washington and Seoul - key security allies who have cooperated on issues such as North Korea for decades.
Opponents counter that it will cause pain to key sectors in both nations - agriculture in South Korea and automobiles in the United States.
GNP legislators had locked themselves in the committee room earlier in the day to head off any opposition attempts to occupy the chamber - the only place where the bill can be introduced.
After a subcommittee review, the bill would be put to a vote at the committee before reaching the full parliamentary session for a final vote.
The GNP says it aims to pass the bill by year's end. The party has a majority in both the committee and in the entire parliament, with 172 seats in the 298-member unicameral National Assembly. But the process is expected to be tough going because opposition parties say they will do whatever possible to stop it.
The Democratic Party says the trade deal should not be approved until the government comes up with better measures to protect farmers and others expected to suffer from increased U.S. imports.
The ruling GNP says the trade pact should be approved as early as possible because South Korea - a major exporting nation - stands to gain much from the deal.
Amid concern the administration of President-elect Barack Obama might ask to renegotiate the agreement, supporters of the pact believe early ratification by Seoul could also put pressure on the U.S. Congress to do the same.
