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

At a White House news conference with his South Korean counterpart, President Obama said Pyongyang will invite even more pressure and isolation if it continues to ignore its international obligations.

Mr. Obama said if North Korea abandons its quest for nuclear weapons and moves toward denuclearization, it will enjoy greater security and opportunity for its people. He said its people have suffered under repressive policies for a very long time.

President Lee Myung-bak said the United States and South Korea speak with “one voice” on the issue of North Korea.

Both presidents 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.

President Lee said he is confident his country's legislature will approve the measure in the near future.

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

In a day filled with the pomp and circumstance for a state visit, Mr. Lee will address a joint meeting of Congress and later be the guest of honor at a White House state dinner.

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.