The Hangyorae Sinmun newspaper published a statement from political, social and religious groups that gathered for an emergency meeting attended by around 1,000 people.
"The reason for the current crisis between the North and South is because of ignoring earlier high-level agreements and the systematic antagonistic policies in regard to the North," the organizers of the protest declared.
Relations between Seoul and the communist North have deteriorated since South Korean President Lee Myung-bak took office in February 2008, rolling back the so-called Sunshine Policy of the previous 10 years.
Participants in the meeting decided to organize mass meetings across the country to foment a national discussion of policy concerning the North.
Tensions are currently high in the region, exacerbated by the North's announcement it will launch what it calls a telecommunications satellite next month and joint South Korean-U.S. military exercises that end on Friday.
South Korean Unification Ministry spokesman Kim Ho-nyoun called for calm last week, saying that Seoul believes Pyongyang needs to take measures to lower tensions, and the UN should actively support the efforts.
After coming to power last February, Lee said he would review agreements reached at the 2000 and 2007 inter-Korean summits, and demand more in return from the North for the economic support provided by Seoul.
North Korea said recently it would scrap all political and military agreements with South Korea, including a non-aggression pact, over its neighbor's "hostile intent." The two countries are still technically at war as their 1950-53 conflict ended in a truce rather than a peace treaty.