South Korea says it has asked the United States to refrain from exporting beef from cattle over 30 months of age, the AP reported.
Tuesday's government announcement follows growing concern over mad cow disease. Older cattle are considered at greater risk of having the terminal ailment.
South Korea agreed in April to reopen its market to U.S. beef after it was blocked for most of the past four and a half years in a ban sparked by the first case of mad cow disease in the U.S.
The government had already said it was delaying the implementation of the agreement, following weeekend street protests and a request from the ruling party.