President Barack Obama has departed for Seoul, South Korea, for an international summit on keeping nuclear materials out of the hands of terrorists.
More than 50 world leaders are expected to attend the gathering on Monday and Tuesday.
Obama's visit comes amid new tension with the North over a planned long-range rocket launch. The U.S. has said the plan jeopardizes a deal to provide American food aid.
Obama's first stop on Sunday morning will be at the Demilitarized Zone separating North and South Korea. His visit is likely to be read by the North as a special show of strength to its new, untested leader.
Air Force One took off from Andrews Air Force Base after midnight.