The move came a day after the South Korean government issued a legal notice of a deal to resume imports of U.S. beef, the final administrative step required to allow shipments to resume to South Korea, previously the third-largest market for American beef.
The quarantine inspection of some of 5,300 tons of U.S. beef from earlier shipments was under way at eight of 17 storage facilities across the country, said the state-run National Veterinary Research & Quarantine Service.
The inspection could take some days and the beef could be on store shelves in about a week, agency spokesman Lee Byung-kwon said, adding that fresh U.S. beef shipments were expected to arrive in South Korea in about a month.
Under the new agreement, imports of U.S. beef will be limited to meat from cattle younger than 30 months, believed less susceptible to mad cow disease.
The deal, however, did not ease public health concerns about U.S. beef and activists vowed to continue their rallies against the government, calling for a complete renegotiation.
Some 1,000 activists from the Korean Confederation of Trade Unions, one of South Korea's two main labor union federations, were at the 17 storage facilities to block delivery of the U.S. beef.
"We will stop the distribution of U.S. beef because it poses danger of mad cow disease," said Woo Moon-sook, a union spokeswoman. The 650,000-member confederation said earlier this month that its members will go on strike July 2.
Demonstrations have dwindled in size since some 80,000 people gathered in central Seoul two weeks ago in the largest recent protest.
On Thursday night, about 3,000 people clashed in Seoul with riot police, who used water cannons and fire extinguishers to repel crowds. Eleven protesters were detained and were being questioned, police said..
U.S. beef has been banned from South Korea for most of the past four and a half years, after the first case of mad cow disease in the U.S. was discovered in late 2003.