South Korea's main opposition Democratic United Party on Saturday urged the government to suspend U.S. beef imports as food safety concerns rise following the latest case of mad cow disease found in a California dairy cow.

South Korea's farm ministry refused to immediately suspend quarantine inspections, which could effectively halt all U.S. beef imports.

The apparent inaction triggered criticism that the government is not delivering on its promise that it will suspend imports in case an outbreak of mad cow disease puts public health at risk here.

"The government has strengthened quarantine checks, but it is questionable how effective it is," Lee Yong-sup, chief policymaker of the center-left party, told a press conference in Seoul.

"All that matter is the government's will," Lee said, adding there is no real legal hurdle if South Korea decides to suspend quarantine inspections and thus temporarily halt imports.

On Friday, interim leader of President Lee Myung-bak's ruling Saenuri Party, Park Geun-hye, urged the government to put quarantine inspections on hold until the safety of U.S. beef is confirmed.

Still, the government said a California dairy cow that contracted mad cow disease, or bovine spongiform encephalopathy ( BSE), was 10 years and seven months old and did not enter the food chain.

South Korea currently imports beef from cattle less than 30 months old with all specified risk materials (SRMs), known to transmit mad cow disease, removed.

Progressive civic groups are planning to hold a rally in central Seoul next Wednesday to protest the government inaction.