North Korea sent a fax to South Korea on Thursday , threatening to `` strike mercilessly without notice '' after protests against the secretive regime this week in Seoul . The message warned that North Korea would strike if `` the provocation against our highest dignity is to be repeated in the downtown of Seoul . '' Earlier this week , on the second anniversary of the death of former North Korean leader , Kim Jong Il , conservative protesters rallied in Seoul , burning effigies of the country 's leaders as well as its flag . Such protests are common during North Korean festivals and anniversaries . The South Korea 's Ministry of National Defense said it sent a response . `` The reply was sent through wired message and in the fax message , we warned that if North Korea is to carry out provocation , we will firmly retaliate , '' said Kim Min-seok , the spokesman for South Korea 's Ministry of National Defense . He added that there have been no significant military movements in North Korea . Pyongyang routinely threatens to retaliate after what it considers `` provocations '' including protests or balloon launches to the north by South Korean groups . Relations between the Koreas have seesawed this year , verging on hostile earlier this year amid a nuclear test in February . This month , the execution of Jang Song Thaek , an advisor and uncle of North Korea 's current leader , Kim Jong Un unsettled its neighbors , prompting speculation about instability in the country 's leadership .
North Korea 's response to South Korea : ' ` ` strike mercilessly without notice '' Protests in Seoul were held over Kim Jong Il 's second anniversary of death . North Korea routinely threatens to strike after what it calls ` ` provocations ''