The South Korean military is planning to ramp up its propaganda broadcasts targeting North Korean troops by doubling the number of loudspeakers along the heavily-fortified border, a report said Wednesday.

Since the North's widely-condemned nuclear test in January, the South has blasted a mix of news, propaganda messages and Korean pop music across the border using giant banks of about 17 loudspeakers.

Yonhap news agency said the number of the loudspeakers would be doubled by the end of the year, and some ageing equipment replaced by new devices capable of broadcasting more than 10 kilometres (6.2 miles) away.

It quoted a Seoul military official who declined to be named. Seoul's defence ministry declined to confirm the report.

"We will make more efforts to erode the morale of the North's troops at the frontline and deliver information (about the outside world) to civilians there," said the official quoted by Yonhap.

North Korean civilians live within range of the loudspeakers.

The move is aimed at punishing Pyongyang for its recent series of provocations, including last month's launch of the new medium-range missile, said the official quoted by Yonhap.

The widely-condemned launch of Musudan missile, which theoretically could reach US military bases in the Pacific including Guam, raised alarm over Pyongyang's capability to deliver a nuclear warhead.

The border propaganda broadcast would carry more criticisms of the North's leader Kim Jong-Un and his "hopeless" policies of pursuing simultaneous development of nuclear arsenal and the economy, according to the official quoted by Yonhap.

The propaganda broadcasts targeting North Korean troops, intensely hated by Pyongyang, have been switched on and off in line with the swings of volatile inter-Korea ties.

Seoul last August resumed them for the first time in 11 years after two of its border patrol soldiers were maimed by mines it said was planted by the North's soldiers.

The broadcasts infuriated Pyongyang, which at one point threatened artillery strikes against the loudspeaker units unless they were switched off.

But the broadcasts came to a halt two weeks later after two Koreas reached an agreement to defuse growing military tension and Pyongyang expressed regret over the mine explosion.