South Korea's defense ministry on Thursday remained cautious over North Korea's rare conciliatory gesture, warning of the possibility that Pyongyang may adopt a "two-track approach" of dialogue and provocations. In his New Year's message, North Korean leader Kim Jong-un called for improved ties with Seoul amid high concerns that the North may stage military provocations against the South as part of its strategy to forge internal unity following the execution of his once-powerful uncle, Jang Song-thaek. In response to the Pyongyang's rare peace offensive, South Korean Defense Minister Kim Kwan-jin warned his military against falling prey to the North's "carrot-and-stick strategy" and ordered soldiers to stay vigilant to counter any provocations, his spokesman Kim Min-seok said. "Looking at past cases, North Korea has taken a conciliatory stance when it had to handle internal problems or carry out reforms due to external factors, and that's when the two Koreas held talks," spokesman Kim said in a briefing. "When the North failed to overcome difficult situations, however, it launched provocations. Under the circumstance, North Korea may take a carrot-and-stick strategy."    Seoul and Washington have put their military on higher alert following Jang's purge, as Pyongyang has a track record of carrying out provocations when experiencing internal instability to divert people's attention and forge unity. Last month, North Korea warned of military strikes against South Korea in anger over a Seoul rally, in which conservative protesters burned effigies of Kim and his father and grandfather, the North's two late leaders, Kim Jong-il and Kim Il-sung.