North Korea has launched around one million propaganda leaflets by balloon towards its southern neighbour amid increased tensions over Pyongyang's recent nuclear test, it has been claimed.

The North's unverified claim of a successful hydrogen bomb test on January 6th has sparked off a new Cold War-style stand-off between the bitter rivals.

South Korea resumed broadcasting anti-Pyongyang propaganda and K-pop songs from border loudspeakers while the North restarted border propaganda operations.

Seoul's defence ministry said the North had been sending balloons loaded with leaflets on a near-daily basis, with some reaching the capital, as well as border areas.

The helium balloons reportedly have timers that cause them to explode and scatter the leaflets.

The tactic has been used occasionally by South Korean activists - triggering angry responses from the North - since the two Koreas agreed to stop psychological warfare in 2004.

South Korean officials believe their upbeat broadcasts will have an impact on frontline troops and residents living in Kim Jong-Un's tightly-controlled secretive state.

But there are doubts that the messages from Pyongyang will have the same cut-through with more affluent citizens of South Korea.

Foreign governments and experts remain sceptical about North Korea's H-bomb claim, although the test is likely to have moved the country closer to having a fully functional nuclear arsenal.

South Korea and the United States are leading calls for the North to be punished, but it is not clear whether China - North Korea's last major ally - would back action at the United Nations.

North and South Korea share the world's most heavily fortified border and are still officially at war since their conflict in the 1950s ended with an armistice rather than a peace treaty.