Dozens of lawmakers from the opposition Democratic Party have been occupying the main hall of the National Assembly since Friday to prevent the ruling Grand National Party from forcing through dozens of bills before year's end, including a controversial free trade deal with the US.

The pact would be the largest for the US since the North American Free Trade Agreement with Canada and Mexico, and the biggest ever for South Korea.

The ruling party, which has control of parliament with 172 seats in the 299-member National Assembly, has said it will unilaterally vote on some 80 bills on Wednesday.

After two days of negotiations to find a compromise ended without success late on Tuesday, National Assembly Speaker Kim Hyong-o invoked his right to order security guards to 'keep order,' Kim spokesman Bae June-young said.

The opposition said it cannot accept Mr Kim's decision, raising concerns about another violent scuffle at the National Assembly.

Earlier in the month, in a bid to force the introduction of the US free trade agreement and other bills, ruling party members set up barricades of furniture near the committee's doors to prevent Democrats from entering the room.

Enraged opposition lawmakers used sledgehammers and construction tools to break down doors blocked by ruling party legislators. GNP lawmakers fought back with fire extinguishers.

South Korea and the US signed the accord calling for slashing tariffs and other barriers to trade in April last year, but the pact still must be ratified by both countries' legislatures.

Opposition lawmakers say the US$29 billion (S$41.7 billion) trade agreement favors major corporations.

The Democrats' floor leader, Won Hye-young, accused the legislature of degenerating into 'a place for a dirty war for President Lee Myung-bak'. -- AP