South Korea's military said Thursday that it takes the death of North Korean leader Kim Jong-un's half brother very seriously and is maintaining a high level of readiness to deal with all threats to national security.In a press briefing, Seoul's Joint Chiefs of Staff said it hasn't detected any unusual movement in North Korea following the suspected murder of Kim's estranged half-brother Jong-nam in Malaysia on Monday. Kim Jong-nam, the elder half-brother of North Korean leader Kim Jong-un. (Yo