The message warned that North Korea would strike if “the provocation against our highest dignity is to be repeated in the downtown of Seoul.”
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.