SEOUL (Reuters) - South Korea’s loudspeaker broadcasts aimed at North Korea push 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 across its border.

North Korea’s fourth nuclear test on Wednesday angered both the United States and China, which was not given prior notice, although the U.S. 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 U.S. 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, which are in line with routine propaganda rhetoric, 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 militarized border, blared criticism of the North’s regime and “K-pop” music. North Korea later responded with its own broadcasts.

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A South Korean military official said Seoul and Washington had discussed the deployment of U.S. 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, U.S. 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 from off the country’s east coast but 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, said a 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 in a short and heavily edited clip.