South Korea's loudspeaker broadcasts aimed at North Korea push the rival countries to the "brink of war," a top North Korean official told a propaganda rally on Friday, in the isolated country's first response to the sonic barrage from across the border.North Korea's fourth nuclear test on Wednesday angered both the United States and China, which was not given prior notice, 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 an ear-splitting propaganda barrage across its border with the North. The last time South Korea deployed the loudspeakers, in August 2015, it triggered an exchange of artillery fire.