South Korea's Defense Ministry says surveillance equipment has detected the trajectories of suspected North Korean rockets and is investigating whether the North has fired at South Korea.

The South said in the statement Thursday it wasn't clear if the North had fired on the border between the rivals, where loudspeakers have been broadcasting anti-Pyongyang propaganda over the past week.

The North had previously said it would retaliate for the South Korean broadcasts critical of alleged North Korean provocations and trumpeting South Korea's democratic system. Seoul started the broadcasts recently in response to what it said were North Korean laid land mines that maimed two South Korean soldiers.