Violence flared outside parliament when thousands of riot police carrying shields and sticks erected a barricade with some 100 buses to block about 3,000 farmers from marching near to the sprawling legislative compound.

Hundreds of angry protestors threw bottles and rocks, triggering a charge by police that left four farmers and one police officer injured, witnesses said.

Dozens of farmers were hauled away by police but the farmers regrouped for a rally demanding the legislature shelve a vote on the Free Trade Accord (FTA) between Chile and South Korea.

Police said 15 protestors were detained after they tried to break into the complex.

Inside parliament, about 30 lawmakers representing farmers surrounded the seat of National Assembly speaker Park Kwan-Yong and blocked the presentation of the bill to a plenary session.

"Shelve the bill," shouted a lawmaker as the speaker tried unsucessfully to push ahead with a vote on the FTA. Last week lawmakers successfully blocked voting when the bill came up for the first time.

"I will not give up my duty as speaker," Park said, warning further delays would hurt South Korean exports.

The ratification of South Korea's first FTA has been delayed since its signing nearly a year ago amid strong protests from farmers who claim it will allow in a flood of cheap Chilean farm produce.

President Roh Moo-Hyun visited the assembly earlier in the day and appealed to rival political parties to ratify the FTA. Roh met with farmers twice this week but failed to win their backing.

Trade officials insist further delays may hurt South Korea's exports and external credit standing, and undermine plans for future trade deals with Japan and Singapore.

Farmers, however, claim the FTA will flood South Korea with cheaper Chilean farm products.

Under the FTA, Santiago would lift tariffs on South Korean cars, trucks, mobile phones and other industrial goods while Seoul would do the same on Chilean copper products, animal feed, wheat, wool, tomatoes and 277 fisheries products.

In November, the South Korean government announced a 119 trillion won (100 billion dollar) aid package over 10 years to help farmers cope with the market opening.