SEOUL, South Korea -- South Korea said it would resume imports of U.S. beef after American and South Korean suppliers agreed to block meat from older cattle, aiming Saturday to soothe health concerns that sparked weeks of demonstrations against new President Lee Myung-bak.

Still, protest leaders argued that the plan doesn't go far enough and staged the latest of their daily candlelight rallies. The rally caused the main intersection in downtown Seoul to be blocked as thousands of riot police prevented demonstrators from marching to the presidential Blue House.

Procedures to put the new import agreement into effect were to start Monday, Trade Minister Kim Jong-hoon said, but it was not clear when American beef would reach South Korean markets.

Lee, a pro-U.S. conservative who took office in February, agreed to allow resumption of American beef imports in April as he sought to improve relations with Washington and pave the way for a larger free-trade deal between the two countries to help reinvigorate the South Korean economy.

The beef-loving South has allowed intermittent U.S. beef imports since banning them in 2003 after the first case of mad cow disease was discovered there.

The April agreement had few restrictions on what meat would be allowed, sparking protests against Lee for caving in to American demands and failing to consider public opinion about health risks. In the wake of demonstrations that drew as many as 80,000 people, Lee replaced all his top advisers, and his entire Cabinet has offered to resign.

The demonstrations have since dwindled, and police said about 6,000 protesters gathered Saturday evening in Seoul.

The U.S. government had refused to renegotiate the April deal because of concern that it could set a precedent for other countries to back out of trade agreements.

Instead, U.S. Trade Representative Susan Schwab said the new arrangement was a "commercial understanding" between U.S. exporters and South Korean importers that only meat from cattle younger than 30 months would be shipped.