President Lee Myung-bak told top military officers Monday to ensure vigilance against North Korea while he is out of the country along with his defense minister for a trip to the United States this week, the presidential spokesman said Monday. Lee is scheduled to depart for Washington on Tuesday for a five-day state visit that includes summit talks with U.S. President Barack Obama and a speech to a joint session of the Congress. The trip is aimed at celebrating the upcoming Congressional ratification of the free trade agreement between the two countries. On Monday, Lee held a meeting with military leaders and instructed them to maintain vigilance against North Korea, saying a strong preparedness will deter provocations, according to presidential spokesman Park Jeong-ha. Attending the meeting were Defense Minister Kim Kwan-jin; Gen. Han Min-koo, chairman of the Joint Chiefs of Staff; and the chiefs of the Army, the Navy and the Air Force, the spokesman said. Lee is scheduled to return home on Sunday.