Lee made his statements during a visit to the Agency for Defense Development, the state-run weapons development agency in the central city of Daejeon, commending researchers there for contributing significantly to South Korea's capability to defend itself.
"Strong (weapons) capabilities are needed to maintain peace, but their purpose lies not in destruction, but in realizing peace and deterring war," Lee said. "If we are strong, (North Korea) cannot make provocations. North Korea makes provocations when we are weak."
Strengthening national self-defense capabilities are a key goal of South Korea, Lee said, stressing the country remains "the only divided nation on the globe" and "faces the world's most belligerent forces" across their heavily armed border.
Concerns have grown that the North could stage additional provocations after last week's failed launch of a long-range rocket. Experts have talked of the possibility of a nuclear test, which will be the North's third, as well as more missile tests and border clashes.
When North Korea shelled the South's border island of Yeonpyeong in November 2010, Lee said he asked China to relay a message to Pyongyang that the South would respond "not in word, but in action" with a counterstrike several times stronger than the North's if it undertakes any additional provocation.
"If we are going to do so, we should have strong weapons and more importantly, strong psychological strength and willpower," Lee said at that time.
The qualities of South Korean-made weapons have improved significantly and they are now exported overseas more often, thus contributing to the country's economy, Lee said Thursday. Many countries, especially those in the Middle East, view South Korean weapons highly, he said.