North Korea ramped up its rhetoric Thursday threatening South Korea with a strike that would come "without notice."

The warning came via fax, and on Friday Seoul responded.

The newest threat came after groups in Seoul rallied on Tuesday to "celebrate" the second anniversary of former leader Kim Jong Il's death.

(SOUNDBITE) (Korean) SOUTH KOREA'S DEFENCE MINISTRY SPOKESMAN KIM MIN-SEOK SAYING:

"We replied through the fax, warning that we will firmly retaliate if North Korea makes provocations."

While China's handball team arrived in North Korea, it also weighed in on the threat calling for restraint.

(SOUNDBITE) (Mandarin) CHINESE FOREIGN MINISTRY SPOKESWOMAN HUA CHUNYING SAYING:

"China opposes any action that will damage the peace and stability of the peninsula. We hope that the relevant parties will maintain calm and restraint, and avoid words and actions that will lead to a state of further escalation of tension on the peninsula."

Tensi