SEOUL, May 23 (Reuters) - South Korea may heed calls in Washington and ease restrictions on U.S. beef with bones after an international agency vouched for the safety of the product, banned due to mad cow fears, a farm ministry official said on Wednesday.

The World Organisation for Animal Health (OIE), which sets guidelines for animal health and meat safety, on Tuesday gave the United States a "controlled risk" status for bovine spongiform encephalopathy (BSE), also known as mad cow disease, at its annual general meeting.

The OIE says deboned beef from cattle under 30 months of age is safe, and with appropriate precautions in a controlled risk country, beef from older animals and bone-in meat can be consumed safely as well.

"We may have to revise safety rules on U.S. beef imports if Washington asks Seoul to follow the OIE guidelines," said the agriculture ministry official, who asked not to be named.

"But the OIE's decision is not mandatory. We will separately re-evaluate the safety of U.S. beef," he added.

The United States once accounted for more than two-thirds of South Korea's beef imports -- around 199,000 tonnes worth about $850 million a year -- but this fell to zero after South Korea banned imports following the first U.S. case of mad cow disease in 2003.

Last year, South Korea, partially opened its market to U.S. meat from cattle less than 30 months old, under the condition that parts it deemed risky, such as bones, were not included.

A trade dispute between two countries has been simmering since last fall, when U.S. beef imports were supposed to resume but South Korea rejected a series of shipments that contained trace bone fragments.

The standoff over trade and import rules has angered U.S. lawmakers, many of whom have threatened to oppose a recently concluded bilateral trade deal unless they see South Korea accept a wider range of American beef.

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