SEOUL, South Korea (AP) _ A top U.S. trade official said Friday that American beef is safe and rejected calls to re-negotiate an accord allowing it to resume beef exports to South Korea.

Fears of mad cow disease have spread among many South Koreans since Seoul agreed last month to resume full-scale imports of U.S. beef for the first time in four years, scrapping nearly all quarantine restrictions imposed against the disease.

U.S. Commerce Secretary Carlos Guiterrez, speaking at a news conference in Seoul, said that every country has a right to ensure the safety of its citizens, but American beef was safe and he didn't see a reason for the beef agreement to be re-negotiated.

``U.S. beef has the highest standard of quality and safety in the world. Second to none,'' he said. ``Beef that we'll be selling to Korea is the same beef that we all buy in the U.S. and that we feed our children in the U.S.''

In recent days, thousands of South Koreans have attended candlelight vigils calling on their government to scrap the beef deal. Faced with fierce opposition, the South Korean government has delayed issuing a government notice on the resumption, a measure required to restart imports.

Imports were initially scheduled to resume earlier this week.

Guiterrez called the delay ``unfortunate'' and said both the U.S. and South Korea should stick to their agreement.

Earlier Friday in a meeting with Guiterrez at the presidential Blue House, South Korean President Lee Myung-bak asked for Washington's cooperation in allaying safety concerns over American beef, according to South Korean media pool reports. Guiterrez nodded at Lee, the reports said.

Lee has said South Korea would halt American beef imports if any new case of mad cow disease breaks out in the United States.

Last month's deal to reopen South Korea's market to American beef came just hours after before South Korean President Lee Myung-bak held his first summit 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.

South Korea suspended imports of U.S. beef after the first American case of mad cow disease appeared in December 2003 in a Canadian-born cow in Washington state.

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, fatal malady.

Guiterrez was in South Korea as part of his Asian trip.