North Korea has started blasting propaganda messages across the heavily militarised border with South Korea in response to similar messages from the South being resumed, officials in Seoul said.

South Korea resumed the psychological warfare broadcasts after 11 years when two soldiers were injured by a landmine allegedly laid by North Korea earlier in August.

Pyongyang denied planting the mines and threatened to launch rocket attacks to blow up the South Korean loudspeakers.

North Korea's own propaganda broadcasts began on 17 August in a section of the eastern part of the border, a South Korean defence ministry official told AP on condition of anonymity.

A defence ministry official told South Korean news agency Yonhap that the purpose of the North Korean propaganda broadcasts was mainly to muffle the sound of those from the South.

Loudspeaker propaganda warfare was called off by the South in 2004 as part of an effort to ease tensions with its neighbour.

But in recent weeks, relations have become worse, with North Korea accusing the South of rehearsing the invasion of the North in joint military exercises with the US. However, South Korea insists the exercises are purely defensive.