SEOUL, South Korea (AP) -- South Korean President Lee Myung-bak pledged Wednesday that his government would immediately halt imports of U.S. beef if it endangered public health.

Fears of mad cow disease have spread among many South Koreans ahead of a planned resumption of U.S. beef imports later this month. Thousands of activists, students and citizens have staged candlelight vigils in recent days calling on the government to scrap an agreement with Washington to restart imports.

Seoul suspended imports of U.S. beef in late 2003 after mad cow disease was discovered in Washington state cattle. It resumed limited imports in April last year, but put them on hold again in October when a shipment arrived containing banned animal parts.

''If the opening of the beef market results in a threat to the people's health, we will immediately suspend imports and work out countermeasures,'' Lee said in a meeting with provincial officials, according to South Korean pool reports.

Later Wednesday, Agriculture Minister Chung Woon-chun told a parliamentary committee that his ministry would halt U.S. beef imports if a new case of mad cow disease was discovered in the United States.

The comments appeared to conflict with the beef deal Seoul signed with Washington last month, under which it agreed not to immediately halt imports if a new case of mad cow disease was discovered in the U.S. Instead, Seoul said it would only halt imports if the Paris-based World Organization for Animal Health downgraded its safety rating for American cattle.

Asked by a lawmaker whether a new suspension of imports might trigger a trade dispute with Washington, South Korea's chief negotiator on beef imports, Min Dong-seok, told the parliamentary committee the U.S. might file a trade suit or the two countries might settle the problem through discussions.

On Tuesday, Min rejected any possibility of renegotiating the deal.

Last month's deal to reopen South Korea's market, including the scrapping of nearly all quarantine regulations previously imposed to guard against mad cow disease, came just hours before President Lee held his first talks with U.S. President George W. Bush. The pact was widely seen as a concession aimed at getting the U.S. Congress to approve a broader trade deal.

Imports of U.S. beef are expected to resume in mid-May and expand in stages.

Scientists believe mad cow disease, or bovine spongiform encephalopathy, spreads when farmers feed cattle recycled meat and bones from infected animals. In humans, eating meat products contaminated with the illness is linked to variant Creutzfeldt-Jakob disease, a rare and fatal malady.