South Korean security officials held an emergency meeting on Sunday to discuss a series of threats from North Korea in recent days, as tensions escalate between the two states, Yonhap news agency reported.
The country's director of national security and ministers from the foreign, unification and defence departments were reportedly present to review the security situation on the peninsula.
Further information on the discussions was not available.
The meeting came after Kim Yo Jong, the powerful younger sister of North Korean leader Kim Jong-un, warned on Saturday that it was time for North Korea to "surely break with" South Korea and threatened to take revenge.
In the past week the North had threatened to cut off all communication lines with South Korea, to close a liasion office along the mutual border and to pull out of a military agreement with the South.
Calls to comply with military pact
On Sunday, South Korea's defence ministry called on the North to comply with the past inter-Korean military pact, the South Korean agency Yonhap reported.
"The defence ministry is taking the current situation gravely, and closely watching moves by the North Korean military," the ministry said in a statement cited by Yonhap, adding that it was ready "in preparation against all situations."
Pyongyang is demanding that Seoul take action against activists who allegedly sent some 50,000 leaflets into the reclusive neighbouring nation criticizing the North Korean leader.
Such campaigns have generally sought to encourage North Koreans to topple the government.
North Korea has threatened military action and accuses Seoul of having done nothing to address the campaign.