Seoul, May 29: South Korea's parliament failed to ratify a free trade deal with the United States before the legislature's four-year term expired on Thursday, lawmakers said.

Opposition parties had boycotted the National Assembly since Monday, demanding President Lee Myung-Bak's government renegotiate a separate deal allowing the resumption of US beef imports.

That deal is a pre-condition for Washington's approval of the free trade agreement (FTA) with South Korea, which some analysts say could eventually boost annual trade between the two nations by 20 billion dollars.

"Sadly, we failed to ratify the FTA in this parliament," said Ahn Sang-Soo, the outgoing floor leader of the ruling Grand National Party (GNP). "We must not waste time any longer. I plead with the United Democratic Party to cooperate and approve the FTA in early months of the incoming legislature," he said, referring to the main opposition party.

"The beef issue is a decisive obstacle to the ratification of the FTA. Unless this obstacle is removed, there will be no FTA," said the United Democratic Party's (UDP's) new floor leader, Won Hye-Young. The South Korean and US governments refuse to renegotiate the controversial beef pact, which has led to mounting protests over fears of mad cow disease.

Thousands of South Koreans have taken to the streets and held candle-light vigils to protest about the supposed dangers of the human form of the disease. But the ruling party said it would announce the resumption of US beef imports later Thursday despite the protests. It agreed in April to lift its intermittent ban on the imports, first imposed in 2003 amid a mad cow scare.