SEOUL, South Korea (AP) -- South Korea's president called Thursday for an end to a long-running dispute over American beef imports, saying it was time for the nation to concentrate instead on overcoming its economic difficulties.

President Lee Myung-bak made the request in a televised speech to cheering ruling party members who packed a Seoul gymnasium to elect their new leaders.

"We are facing dual challenges at home and abroad," Lee said. "Our law and order have been ignored and our economic difficulties have been deepened. We must wisely and squarely surmount these challenges."

Lee said he would not tolerate illegal, violent protests against U.S. beef imports, but would listen more carefully to public opinion at peaceful rallies.

Lee, who took office in February, said his government would make "a fresh start" to win back public confidence.

Members of his Grand National Party elected Park Hee-tae, a five-time lawmaker and close associate of Lee, as its new chairman. Park said the party will dedicate itself to reviving the slowing economy and restoring public support.

Lee's government agreed in April to lift a ban on imports of U.S. beef, prompting weeks of street rallies over health concerns and a perception that he had backed down too easily to American pressure. Amid nose-diving popularity, he was forced to replace top advisers and his entire Cabinet has offered to resign.

His government negotiated an amendment to the import deal last month to limit shipments to beef from cattle younger than 30 months, believed less susceptible to mad cow disease.

Daily candlelight protests in Seoul by up to 80,000 people have dwindled in size but turned violent last week when the government began inspecting U.S. beef. More than 200 protesters and riot police were injured in a weekend rally.

About 3,000 people protested against U.S. beef Thursday evening in central Seoul, according to police. No clashes were immediately reported.

U.S. beef went on sale earlier this week but is not widely available because large supermarket chains and restaurants are reluctant to sell it for fear of a public backlash.

On Thursday, consumer groups launched a boycott of American beef, vowing to make the country free of mad cow disease.

"We will oust American beef feared to carry mad cow disease from our dinner tables without fail," the Korean Women's Association United and four other coalitions of civic groups said in a statement.

A group of lawmakers also introduced a bill Thursday that would ban American beef from school meals until public concerns about mad cow disease are resolved.

South Korea banned imports of American beef in 2003, when the first of three cases of mad cow disease was discovered in the United States. Before the ban, South Korea was Nebraska's second-largest beef market, valued at $108 million annually.

Both the U.S. and South Korean governments insist American beef is safe.

Associated Press writer Jae-soon Chang contributed to this report.