The letter from the isolated Communist country's National Defense Commission, carried by the official Korean Central News Agency, urged South Korea to accept its proposals which included a call to end the inter-Korean military hostility as well as to cancel the joint military drills between the South and the United States set to begin next month.
The letter also said the gestures are not a prelude to provocation, South Korea's Yonhap News reported.
South Korea has said it will not cancel the planned two-month long military drills. Earlier this month, a spokesman for the North's Committee for the Peaceful Reunification of Korea had warned the military exercises could push the situation on the Korean Peninsula to a catastrophe as they could be a rehearsal for a nuclear war against it.
The North Korean letter again renewed its call to cancel the drills and urged Seoul to refrain from rashly rejecting its proposals, Yonhap said.
"Our important proposal is neither a deceptive peace overture nor propaganda warfare," the letter said.
Yonhap said South Korean Unification Minister Ryoo Kihl-jae had dismissed the North's offer as nothing but "propaganda and rhetoric."
Analysts have warned North Korea has a track record of carrying out provocations after making conciliatory gestures toward South Korea, such as its third nuclear test in February last year which took place a month after a call for improving inter-Korean ties.
CNN quoted the North's letter also as saying the defense commission promised to work to "completely halt hostile military acts, realize the reunion of separated families and relatives ... and re-energize multifaceted North-South cooperation and exchanges."
The commission said inter-Korean relations will improve on a solid basis "only when both sides take realistic measures to prevent impending nuclear disasters with concerted efforts of the Korean nation."