He said his incoming government will engage in full inter-Korean cooperation if Pyongyang faithfully implements agreements reached at six-nation nuclear talks.
Lee said he aimed to seek a prompt solution to the nuclear issue.
Outgoing South Korean President Roh Moo-hyun met with North Korea's Kim Jong-il for the two nations' second-ever summit last October.
Lee, who is expected to take a tougher line on North Korea, has said he will agree to continue the generous flow of aid to the impoverished country seen under his predecessor, on the condition that Pyongyang meet all its obligations to scrap its nuclear program.
Korea "is the only divided nation on the face of the earth. We cannot but take defense and security seriously," Lee said.
The agency quoted diplomatic sources as saying that South Korea hopes to see the full denuclearization of North Korea by 2010, a goal which will depend largely on the communist state's will to end decades of isolation.
Former Seoul mayor and CEO of auto giant Hyundai Lee Myung-bak won a landslide victory at the December 19 polls. He received strong public support for his economic plans, despite a criminal probe into alleged stock manipulation.
Under a February deal made with the other five countries at the six-nation talks, North Korea was to decommission all of its nuclear facilities in Yongbyon and submit a complete list of its nuclear programs by the end of 2007. Pyongyang was promised economic and diplomatic incentives in return for the measures.
