South Korea expressed doubt Friday over the North Korean leader's rare peace offensive as it urged Pyongyang to make serious efforts to denuclearize itself, the Seoul-based Yonhap News Agency reported. "We have no choice but to question the sincerity" of Kim's conciliatory gesture, Unification Ministry spokesperson Kim Eui-do said in a comment carried by Yonhap. The comment came two days after North Korean leader Kim Jong-un called for "a favorable climate" to improve ties with South Korea and pledged to make aggressive efforts to strive for better relations in his New Year's message. The ministry, which handles inter-Korean affairs, cited Pyongyang's track record of carrying out provocations and slandering South Korea as a reason for caution on its peace call. Last year, the North also issued a similar charm offensive before taking a series of provocative actions, including a third nuclear test, threats of nuclear war and unilateral closure of an inter-Korean factory park. The ministry said the North is to blame for worsening the inter-Korean ties. "North Korea should show sincere attitude to build trust and take sincere efforts for denuclearization," the ministry said. North Korea has rejected repeated international calls to abandon its nuclear weapons programs. South Korean Defense Minister Kim Kwan-jin ordered troops to stay vigilant to counter any possible provocations from North Korea, according to the report. In December, North Korea warned of military strikes against South Korea in anger over a Seoul rally, in which conservative protesters burned effigies of Kim Jong-un and his late father and grandfather.