South Korea’s loudspeaker broadcasts aimed at North Korea have pushed the rivals to the “brink of war,” a top North Korean official has told a propaganda rally, in the isolated country’s first official response to the sonic barrage from across its border.

North Korea’s fourth nuclear test on Wednesday angered both the US and China, which was not given prior notice of the move, although the US government and weapons experts doubt the North’s claim that the device it set off was a hydrogen bomb.

In retaliation for the test, South Korea on Friday unleashed a ear-splitting propaganda barrage.

The last time South Korea deployed the loudspeakers, in August 2015, it triggered an exchange of artillery fire.

“Jealous of the successful test of our first H-bomb, the US and its followers are driving the situation to the brink of war, by saying they have resumed psychological broadcasts and brought in strategic bombers,” Kim Ki-Nam, head of the ruling Workers’ Party propaganda department, said at Friday’s rally.

State media published images of the rally, which appeared to show thousands of people gathered in central Pyongyang, holding signs glorifying leader Kim Jong-Un, whose birthday was also on Friday.

Kim Ki-Nam’s comments were the North’s first official response to the South’s broadcasts, which it considers insulting.

The broadcasts, in rolling bursts from walls of loudspeakers at 11 sites along the heavily-militarised border, blared criticism of the North’s regime and “K-pop” music.

North Korea later responded with its own broadcasts.

Strategic weapons

A South Korean military official said Seoul and Washington had discussed the deployment of US strategic weapons on the Korean peninsula after the test, but declined to give details.

Media said these could include B-2 and B-52 bombers, and a nuclear-powered submarine.

On Thursday, US secretary of state John Kerry said he had told Chinese foreign minister Wang Yi that China’s approach to North Korea had not succeeded.

Wang also held talks with his South Korean counterpart, Yun Byung-se.

Yun pushed Wang to “sternly punish” North Korea over the test, the South Korean foreign ministry said.

China is North Korea’s main economic and diplomatic backer, although relations between them have cooled in recent years.

South Korea’s nuclear safety agency said it had found a minuscule amount of xenon gas in a sample found off the country’s east coast, but it needed more analysis and samples to tell if the trace came from a nuclear test.

South Korea said TV footage released by the North on Friday of what appeared to be a submarine launch of a ballistic missile was probably manipulated.

The deployment of such a weapon is some years away, according to a South Korean military official who asked not to be identified.

The images showed Kim Jong-Un on the deck of a vessel watching a missile emerge from the water.

Reuters