SEOUL (AFP) - South Korea said on Thursday (Jan 7) it would resume propaganda broadcasts into North Korea, a tactic that prompted Pyongyang to threaten military strikes when it was last employed during a cross-border crisis last year.

The decision to resume the high-decibel broadcasts using massive batteries of speakers on the heavily militarised frontier was taken in response to the North's latest nuclear test on Wednesday (Jan 6), an official at the presidential Blue House said.

"The North's fourth nuclear test is a wanton violation of its international obligations ... and a grave violation of the inter-Korea agreement on August 25," the official said.

"So the South Korean government decided to resume the border broadcast into the North as of noon (11am Singapore) on Friday (Jan 8)," he added.

The Aug 25 agreement ended an extended and increasingly hostile standoff that had brought the two Koreas to the brink of an armed conflict.

After North Korea "expressed regret" for mine blasts that maimed two patrolling North Korean soldiers, the South turned off the banks of loudspeakers that had been blaring music and propaganda messages across the border for two weeks.

But the deal included a formula agreed by both sides that the loudspeakers would remain unplugged "unless an abnormal case occurs".

The South's decision to resume was presumably based on the argument that Wednesday's (Jan 6) test qualified as "abnormal." At the height of last year's crisis, the North had issued an ultimatum for the South to halt its "psychological warfare" or face imminent attack.