South Korea began a high-decibel propaganda barrage across its border with North Korea on Friday in retaliation for what it claimed as a nuclear test, while the United States called on China to end “business as usual” with its ally.

Friday's moves came as the international community struggled to find common ground on how best to penalize North Korea following its announcement two days ago that it had successfully tested its first hydrogen bomb. The claim has been met with condemnation and skepticism.

South Korea's Yonhap news agency reported that frontline troops, near 11 sites where propaganda loudspeakers started blaring messages at noon, were on highest alert. In the past, similar broadcasts have angered North Korea.

Yonhap said Seoul had deployed missiles, artillery and other weapons systems near the border on Friday to swiftly deal with any possible North Korean response. South Korea's Defense Ministry couldn't confirm the reports and the military banned foreign media from the border ahead of the broadcasts.

The broadcasts include popular Korean pop songs, world news and weather forecasts as well as criticism of the North's nuclear test, its troubled economy and dire human rights conditions, according to Seoul's Defense Ministry.

Among the songs on Friday's playlist was “Bang, Bang, Bang” a recent hit by top K-pop boy band, Big Bang. Their resumption revives psychological warfare tactics that date to the 1950-53 Korean War.

“We're putting out critical messages about Kim Jong-un's regime and its fourth nuclear test, saying North Korea's nuclear weapons development is putting its people in more difficult times economically,” a military official said.

North Korea, in return, started its own loudspeaker broadcasts on the shared border, the South's Yonhap News Agency said on Friday.

The broadcasts, which North Korea considers an act of psychological warfare, are expected to draw a furious response in part because Friday is believed to be the birthday of North Korea’s leader Kim Jong Un and the broadcasts are meant to raise questions about the infallibility of the ruling Kim family.

Before the broadcasts began, U.S. Secretary of State John Kerry has urged China to end “business as usual” with North Korea.

Kerry told reporters in Washington that he spoke by phone Thursday with Chinese Foreign Minister Wang Yi. He said that China's approach to North Korea had failed. The U.N. Security Council that has pledged new sanctions against North Korea after its purported hydrogen bomb test on Wednesday. China has a pivotal position as it is a permanent council member and the North's main trading partner.

China said after the call with Kerry that it was willing to communicate with all parties, including the United States.

“Wang Yi stressed that China has staunchly dedicated itself to the goal of the peninsula's denuclearization and to maintaining peace and stability on the peninsula,” the Chinese Foreign Ministry said in a statement.

It may take weeks or longer to confirm or refute the North's claim that it successfully tested a hydrogen bomb, which would mark a major and unanticipated advance for its still-limited nuclear arsenal.

Later Friday, South Korea was to announce the results of its first round of investigations of samples collected from sea operations to see if radioactive elements leaked from the North's test, according to the Korea Institute of Nuclear Safety.

When South Korea briefly resumed propaganda broadcasts in August after an 11-year break, the two Koreas exchanged artillery fire, followed by threats of war.

“We urge South Korea to exercise restraint,” British Foreign Secretary Philip Hammond said during a visit to Japan, after the South resumed the broadcasts. “It is simply rising to the bait.”

The sound from the speakers can carry for 6 miles into North Korea during the day and more than twice that at night, Yonhap reported.

Wire services