South Korea's President Lee Myung-bak has told his nation it must unite in the face of military aggression from the North, because its survival is at stake.
In a national radio address Mr Lee also said that if South Koreans are afraid of war, "we can never prevent war".
Tension on the Korean peninsula is at its highest since the end of the Korean War in 1953.
On Sunday it was announced that the South Korean and Chinese defence ministers would meet in Beijing in February.
No details of the talks have been issued, but the BBC reports the two sides are expected to discuss what Seoul describes as North Korea's hostile acts in recent months.
These include the Yeonpyeong shelling on 23 November and the sinking of a corvette, with the deaths of 46 crew, on 26 March.
Strong rhetoric traded
Earlier this week, Seoul and Pyongyang again traded strong rhetoric. The North threatened a "sacred war" against the South, which has been holding live-fire drills near the border, and the South warned of a "powerful response" to any attack.
On Friday, state TV in North Korea aired a programme in which soldiers boasted about the shelling of Yeonpyeong.
North Korea carried out nuclear tests in 2006 and 2009.