SEOUL, May 2 (Reuters) - South Korea on Friday rejected charges it was ignoring safety concerns by allowing U.S. beef back into the country and said it could not renege on an agreement it struck with Washington.

South Korea in mid-April said it will open its market wider to American beef. U.S. lawmakers have said a separate, sweeping bilateral free trade deal would not make it through Congress until Seoul made concessions on beef.

South Korean farmers, who stand to lose out to cheaper imports, and consumers worried if the U.S. product was free of mad cow disease, have criticised the beef agreement, saying new President Lee Myung-bak kowtowed to Washington.

"It is regrettable that safety questions have been raised as if they were facts but there are no scientific basis to them," Agriculture Minister Chung Woon-chun told a news conference.

One local TV station claimed Koreans carry a special gene that makes them more susceptible to mad cow disease. A panel of physicians who attended the Friday's news conference denied those suggestions.

Lee said on Friday some were politicising safety questions to incite fear.

A ministry official said it was all but impossible to reopen discussions with the United States unless there was a change in U.S. mad cow "controlled risk" status under World Organisation for Animal Health (OIE) guidelines.

South Korea, once the third-largest import market for U.S. beef, imposed a blanket ban on imports in 2003 following an outbreak of mad cow disease. It later eased the ban by allowing imports of boneless beef from cattle younger than 30 months.

U.S. beef, under the new rules, will be allowed in as early as mid-May but South Korea said it will stop imports if the United States lost its "controlled risk" country status. The exports could be worth about $1 billion a year, experts said.

Lee, who took office in February, has seen his support rate sink in recent weeks to 35 percent, and an online petition drive to impeach him has collected more than half a million signatures.

The beef deal was announced during his first trip overseas since taking office, shortly before he met President George W. Bush at the Camp David retreat. (Reporting by Jack Kim; Editing by Jon Herskovitz and Alex Richardson)

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