After North Korea detonated what is suspected to be a hydrogen bomb on September 3, the US spearheaded the toughest sanctions levied to date against Pyongyang by the UN Security Council. But after the second round of "historic" sanctions within a month, the detrimental effect of partially cutting off fossil fuel supplies, freezing individual assets and preventing textile trade are seen by many observers as being just another incremental response to a belligerent regime clearly determined at all costs to continue developing nuclear weapons.

Friday's ballistic missile launch over Japan, the second over Japanese territory in two weeks, also indicates that sanctions have yet to deter Pyongyang's provocations. The launch also presents a direct challenge to the US and China to somehow create a united front against the North.

The US had originally pushed for a tougher sanctions regime - including a full oil embargo and travel ban for North Korean officials - but had to soften its demands to ensure full cooperation from China.

Read more: 'Ultimate sanction' - Will cutting off oil bring North Korea to its knees?

Aside from the self-congratulation earlier this week in Washington over another unanimous UN vote, the rift between Chinese and US interests moving forward on North Korea is clear, as it is apparent that Beijing is continuing to stop short of taking action that would topple the Kim Jong Un regime.

This, combined with North Korea's constant weapons testing and rapid advancements in capability, is exacerbating the already tense relationship between the US and China.

Read more: What is China's role in the North Korean crisis?

Dialogue - made in China

Following the UN Security Council resolution on September 11, China's official Xinhua news agency released a commentary stating that the Trump administration was making a mistake by pursuing deeper sanctions rather than seeking diplomatic engagement with North Korea.

"The US needs to switch from isolation to communication in order to end an 'endless loop' on the Korean peninsula where nuclear and missile tests trigger tougher sanctions and tougher sanctions invite further tests," Xinhua said.

China has been advocating a so-called "freeze for freeze" strategy, where the Kim regime agrees to cease all weapons testing and missile launches in exchange for the US diminishing its military footprint on the peninsula and ceasing all joint military exercises with the South.

The US has roundly rejected any new forms of "freeze" agreements that it considers would weaken its strategic posture on the Korean peninsula. Two similar deals struck between the US and North Korea during the Clinton and Bush administrations fell through after they were not honored by Pyongyang.

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US dollars for Chinese compliance

The US is dubious of China's commitment to enforcing sanctions, as Chinese individuals and companies have been found in the past to be in violation of UN sanctions for not cutting ties with North Korea.

After the last round of UN sanctions against Pyongyang in August, the US issued an additional set of sanctions against Chinese individuals and companies for allegedly aiding the North Korean weapons program.

A commentary in the Chinese state-run newspaper Global Times responded by accusing the US of "severely violating" international law by sanctioning Chinese companies and individuals, while maintaining that China "strictly implements" UN Security Council resolutions.

"Who grants Washington the right to make judgments on which companies violate UN Security Council resolutions?" said the commentary.

The new round of sanctions on Monday makes it illegal for foreign firms to form commercial joint ventures with North Korean entities.

On Tuesday, the US Treasury Secretary Steve Mnuchin told media that if China didn't follow the UN sanctions on North Korea, the Trump administration would pursue additional sanctions on Beijing to cut off access to the US financial system.

"If China doesn't follow these sanctions, we will put additional sanctions on them and prevent them from accessing the US and international dollar system, and that's quite meaningful," Mnuchin said.

Ely Ratner, a former national security advisor with the Obama administration and a China expert at the US Council on Foreign Relations, told DW that the Trump administration would likely impose additional secondary sanctions on Chinese firms, banks, and individuals that continue doing business with North Korea illegally in violation of UN sanctions.

"The Chinese government won't like this, but it only has itself to blame for not enforcing UN Security Council resolutions that it voted for," said Ratner.

A Trump administration official told Reuters news agency that any such "secondary sanctions" on Chinese banks and other companies were on hold for now to give China time to show it was prepared to fully enforce the latest and previous rounds of sanctions.

Read more: North Korea sanctions: EU targets main exports with an expanded blacklist

China won't back down

But even if China complies with what the US considers are watered-down sanctions, the bottom line is that it is not in China's national interest to eliminate the Kim regime in Pyongyang. Observers agree that Beijing is less concerned about the North's weapons program than it is about a US-sponsored, re-united Korean peninsula.

"China doesn't want the DPRK to collapse because that would leave many uncertainties regarding its weapons, refugees and a US base at its doorstep," Eduardo Araral, Vice Dean of research at the Lee Kuan Yew School of Public Policy in Singapore, told DW.

Araral added that the US would not be able to handle North Korea without cooperation from China. "US-China ties are so intertwined that the US cannot continue hurting China, for example on trade, without hurting itself," he said.

A post- Kim peninsula?

One of the major hurdles in preventing a united front from the US and China in dealing with the Kim regime, is the uncertainty of the geopolitical outcome on the Korean Peninsula if the North were to collapse and be folded into the South.

US and Chinese interests do merge, however, in that both do not want a nuclear-ready North Korean military machine, and China especially does not want nuclear war in its backyard. It should be noted that China does not necessarily have friendly relations with North Korea. Chinese President Xi Jinping has never met with Kim Jong Un and there are signals that China is willing to take a tougher stance on the regime. Nevertheless, these considerations are outweighed by a tangle of Chinese geopolitical interests.

For China to accept a united Korean peninsula, they would need to be assured that the US would demilitarize in the region and that a new regional security architecture could be created with Beijing's interests at the helm. This scenario presents a problem, not only for US interests, but also for Japan and South Korea.

Noah Feldman, author of "Cool War: The United States, China, and the Future of Global Competition" and professor at Harvard Law School, told a debate organized and broadcast online by Intelligence Squared on September 13, that China presented a "structural problem" for a unified Korea. US security guarantees on the Korean peninsula would be essential for South Korea and Japan to agree to a new geopolitical structure in Northeast Asia, which is something that China won't agree to.

"Countries are living under the Chinese economic sphere of influence, while depending on the US as a security guarantor. They are playing both ends against the middle and that has worked for those countries," said Feldman during the debate.

It is worthwhile noting that the only time the US and China have engaged in direct conflict was on the Korean peninsula in 1950, after the Chinese People's Volunteer Army entered the Korean War to fight on behalf of North Korea against a US-led coalition defending the South. And more than 65 years later, it seems that again decisive action from the Chinese is necessary to tip the balance in Northeast Asia.