WASHINGTON (TIP): The United States called on China to end “business as usual” with its ally North Korea after Pyongyang defied world powers by saying it had tested a hydrogen bomb, while South Korea prepared to retaliate by broadcasting propaganda across the border.

South Korea, which has grown increasingly close to China in recent years, said its foreign minister would speak with his Chinese counterpart later on January 7.

US secretary of state John Kerry said on Thursday he had made clear in a phone call with Chinese foreign minister Wang Yi that China’s approach to North Korea has not succeeded.

“China had a particular approach that it wanted to make, that we agreed and respected to give them space to implement that,” Kerry told reporters. “Today in my conversation with the Chinese I made it very clear that has not worked and we cannot continue business as usual.”

China is the North’s main economic and diplomatic backer, although relations between the two Cold War allies have cooled in recent years.

China’s foreign ministry said after the call with Kerry that Beijing 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 decentralization and to maintaining peace and stability on the peninsula,” the Chinese foreign ministry said in a short statement.

South Korea’s foreign ministry had requested a phone call with Wang since directly after North Korea announced on Wednesday it had tested a hydrogen bomb, the South’s Yonhap News Agency said. However, the call had been delayed due to China’s “internal scheduling”, it said, citing an unnamed official.

South Korea’s propaganda broadcasts by loudspeaker across the heavily militarized border, known to infuriate the leadership of isolated North Korea, were due to begin at noon local time (1000 ET) on January 7.

The last time Seoul deployed the speakers, in retaliation for a landmine blast in August that wounded two South Korean soldiers, it led to an armed standoff and exchange of artillery fire.

South Korea heightened military readiness to its highest level at locations near the loudspeakers, and Seoul vowed to retaliate against any attack on the speakers.

The South Korean city of Paju, which sits along the border with North Korea, suspended tours of the Demilitarized Zone (DMZ) at the military’s request.

Seoul had also raised South Korea’s cyber security alert level. Yonhap also reported that North Korea had boosted troop deployments and raised its surveillance of the South.

“Nuclear conundrum” Wednesday’s test angered both the United States and China, which was not given prior notice, although the US government and weapons experts doubt Pyongyang’s assertion that the device it exploded was a hydrogen bomb.

The vast majority of North Korea’s business dealings are with China, which bought 90 percent of the isolated country’s exports in 2013, according to data compiled by South Korea’s International Trade Association.

Kerry said he and Wang agreed to work closely to determine what measures could be taken given increasing concerns about the nuclear test. He said America has a “firm and continued commitment to regional security and global nonproliferation”.

The Global Times, an influential tabloid published by China’s ruling Communist Party’s official People’s Daily, said in an editorial it was unfair to expect China alone to bring about change in Pyongyang.

“There is no hope to put an end to the North Korean nuclear conundrum if the US, South Korea and Japan do not change their policies toward Pyongyang. Solely depending on Beijing’s pressure to force the North to give up its nuclear plan is an illusion,” it said. “The China-North Korea relationship should not be dragged into antagonism. Beijing has participated in previous sanctions on the North. Whether China will take tougher measures hinges on the decision of the UN Security Council,” it said.

US Republicans and Democrats in the House of Representatives could join forces in a rare display of unity to further tighten sanctions on North Korea.

(Reuters)