U.S. President Barack Obama says North Korea continues to pose a direct threat to the United States and South Korea.

President Obama said further provocation from North Korea will lead to greater isolation for the nation. He said the country will enjoy greater security and opportunity for its people if it abandons its nuclear program.

Mr. Obama spoke Thursday, as he hosted South Korean President Lee Myung-bak at the White House for a state visit.

Presidents Obama and Lee both hailed a U.S.-South Korea free trade agreement that the U.S. Congress passed late Wednesday. The two leaders said the agreement will support jobs and increase trade between the two allies. The free trade deal is expected to be worth billions of dollars to both countries' economies. It still needs to be approved by South Korea's legislature.

President Lee arrived at the White House Thursday morning for a formal welcoming ceremony. Mr. Obama said the alliance between the nations has never been stronger.

Later Thursday, Mr. Lee will be afforded the rare honor of addressing a joint meeting of Congress, reflecting the growing economic and strategic relations between the United States and South Korea.

Mr. Lee was dining with President Obama at a Korean barbecue restaurant outside Washington when they received word late Wednesday that the U.S. Congress had approved the trade deal. The South Korean president now faces intense pressure to get approval of the agreement through his own country's legislature.

President Lee is to accompany President Obama on a visit Friday to a General Motors car plant in Detroit. Mr. Obama has said he would like to see Koreans driving U.S.-built cars the way many Americans drive Korean cars.

Wednesday, Mr. Lee visited the Pentagon for talks with Defense Secretary Leon Panetta and members of the Joint Chiefs of Staff. Mr. Lee said at the White House that he also visited the Korean War Veterans Memorial in Washington to pay tribute to the Americans who fought and died in the conflict.