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Story highlights

Relations between China and North Korea have been cooling

However, THAAD missile defense complicates China's response

(CNN) —  

North Korea’s latest nuclear test will pile the pressure on China – the country’s economic benefactor and only real ally – to rein in Kim Jong Un’s regime.

But, even if it were willing, Beijing increasingly appears unable to influence its unruly neighbor.

“China doesn’t have any sticks with North Korea,” says Tong Zhao, an associate at the Carnegie Tsinghua Center for Global Policy in Beijing.

“It won’t cut off economic ties completely; that would make China vulnerable to North Korea threats… and a potential collapse.”

Chinese foreign ministry spokeswoman Hua Chunying declined to say Friday if China had received advanced notice of North Korea’s nuclear warhead test.

Tests getting are getting more powerful

’Slap in the face’

Relations between Pyongyang and Beijing have been frosty since Kim Jong Un succeeded his late father as dictator, promptly purging several key government figures – such as his uncle Jang Song Thaek – with strong ties to China.

Kim has never visited China as leader, nor has he met President Xi Jinping, despite reportedly lobbying to do so for several years.

Mike Chinoy, former CNN international correspondent and the author of “Meltdown: The inside story of the North Korean nuclear crisis,” called January’s test of a hydrogen bomb a “real slap in the face” for China.

In March, China joined the international community in placing the toughest ever sanctions on the country.

Zhao says that China largely implemented them – stopping its banks from operating in North Korea and cracking down on the export of military or dual use materials.

“After the January test, my view was that North Korea wouldn’t dare do another one. The international community was outraged,” said Zhao.

“The UN was able to pass the strictest sanctions ever, which many thought would make the regime really unstable.”

Hua declined to say Friday if China would support new, tougher sanctions.

What can China do about nuclear North Korea?

Beijing dilemma

Complicating matters this time around is China’s opposition to the US THAAD missile defense system, which is being deployed to defend South Korea from missile attack.

Beijing views it as an attempt to shift the regional balance of power in favor of US allies and contain China.

This makes North Korea’s role as a buffer between China and U.S. ally and mutual defense signatory South Korea more valuable to Beijing, said Zhao, giving North Korea more wiggle room to make provocative moves without risking its ties with China.

“(North Korea) is being opportunistic and taking advantage of the current troubles between China and the United States,” said Zhao.

This makes it much more difficult for China to respond and curtails what sway they may have had.

“Previously China saw North Korea as a liability. But now, if China sees a great threat from the US, its value could rise. At least, if it helps distract the US from other issues like the South China Sea,” he said.

In the end, the Chinese calculus is that instability in North Korea is more dangerous than a North Korea with bombs.

“China will do the easy things – they will reprimand North Korea and agree to start discussions at the UN,” said Zhao.

“But China is now in a worse position to have an influence (on North Korea.)”

CNN’s James Griffiths contributed to this report