SEOUL , South Korea ( CNN ) -- Thousands of protesters battled riot police in downtown Seoul early Sunday morning after a rally opposing South Korea 's decision to import U.S. beef turned violent . More than 100 were wounded , the state news agency reported . Police use a water cannon to disperse protesters during a rally against U.S. beef imports in Seoul on Sunday . Clashes broke out after more than 15,000 protesters headed toward the presidential office , news agency Yonhap said . The demonstrators used ropes to pull down police buses that had been parked around the presidential office to block the marchers from entering . Many carried steel pipes and hurled rocks at officers . Police fired back with water cannons and fire extinguishers . South Koreans have protested regularly since April when the government announced it would resume importing beef from the United States after a five-year ban . That ban was instituted over a case of mad cow disease in 2003 . Watch police and protesters battle in streets » . The widespread public protests essentially paralyzed the government of President Lee Myung-bak , who replaced seven top aides this month and plans to reshuffle his cabinet . After a series of negotiations , Seoul and Washington came up with a revised agreement on June 21 -- one that limits imports to cattle less than 30 months old . Animals more than 30 months old are considered at a greater risk for mad cow disease , which can be transmitted to humans . The revised agreement also excludes the import of certain parts believed more susceptible to mad cow disease . The initial deal would have allowed the import of all U.S. beef imports . U.S. Secretary of State Condoleezza Rice , during a visit to visit to Seoul as part of an Asian tour , emphasized Saturday that American beef is safe and that her government will continue efforts to win consumer confidence . The assurance did little to placate demonstrators who took to the streets late Saturday night , leading to the latest riots . Scientists believe mad cow disease spreads when farmers feed cattle recycled meat and bones from infected animals . The U.S. banned recycled feeds in 1997 . Eating meat products contaminated with the illness has been linked to variant Creutzfeldt-Jakob disease , a rare and fatal malady in humans . Until the 2003 ban , South Korea was the third-largest market for U.S. beef exporters . The U.S. beef industry has lost up to $ 4 billion since the market closed , according to the U.S. Meat Export Federation . The imports are expected to resume this month .
About 15,000 people attended street demonstration in Dhaka . It turned violent after some protesters tried to drag away police officers . The police used water cannons and sprayed fire extinguishers to repel them .