A regional police official was quoted by the Yonhap News Agency as saying demonstrators were blocked from deploying leaflets across the border into North Korea.
"We have placed an entry ban on civilians and vehicles taking into consideration safety concerns over North Korean warnings, clashes between anti- and pro- civic groups and complaints from residents," the official said on condition of anonymity.
Pyongyang last week said it would conduct a "merciless military strike" against anti-government activists near the border.
In 2000, both sides agreed to halt psychological operations near the border and, in 2004, both governments pulled down propaganda along the shared border.
The South Korean Defense Ministry in July said troops along the border discovered leaflets along the border that carried statements blasting alleged attempts to destroy a statue of late North Korea leader Kim Il Sung.