President Lee Myung-bak and U.S. President Barack Obama have agreed to take unified action against North Korea's planned rocket launch through close cooperation with other countries.

Lee and Obama on Thursday held their first meeting in London on the sidelines of the G20 financial summit.

During the 30-minute discussion, the two leaders agreed to seek U.N. actions if North Korea goes ahead with a rocket launch, calling it a violation of the U.N. Security Council Resolution 1718. But they agreed to focus on economic sanctions to punish the North rather than pursuing any military response.

The two leaders also agreed to extend a 30-billion-dollar credit swap line that expires in October and pursue the swift approval of a bilateral trade agreement.

Mr. Lee will visit Washington at an early date to have further discussions on strengthening bilateral relations.