"The North initially operated its own loudspeakers at two locations and has now expanded to several locations. In fact, the anti-South loudspeaker broadcasts appear to be coming from every location where we are broadcasting," a government source told the Yonhap news agency.
According to the media outlet, the North Korean messages mainly promote the country’s leader Kim Jong Un and criticize South Korean President Park Geun-hye.
Seoul is said to be currently broadcasting propaganda from 11 points.
Last week, Pyongyang announced it had successfully tested a hydrogen bomb. The international community has condemned the test as provocative and undermining stability in the region.
North Korea declared itself a nuclear power in 2005 and conducted nuclear tests in 2006, 2009 and 2013, having earlier withdrawn from the Nuclear Non-Proliferation Treaty.