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, Reuters reports.

North Korea's fourth nuclear test on Wednesday, January 6, 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.

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.