LONDON - U.S. President Barack Obama told South Korean President Lee Myung-bak on Thursday problems remain on a stalled free trade deal between the two countries but that he wants to make progress, a U.S. official said.

President Obama said that he understood there were difficulties on both sides on moving forward, but he said that he does want to make progress and staff should discuss how to move forward, the official said after the two leaders met on the sidelines of a G20 economic crisis summit in London.

Obama also invited Lee to visit Washington for talks in mid-June, the official said.