North Korea's unprecedented barrage of missiles is underscoring the costs of Washington's tensions with Beijing, since China has shown little appetite for additional sanctions over the country's nuclear program.

China, along with Russia, played a critical role in approving United Nations sanctions on their neighbor after Kim Jong Un tested an atomic bomb and launched a missile designed to carry warheads to the U.S. five years ago. There's little prospect of finding such unity on the UN Security Council now, even though North Korea has fired about 100 ballistic missiles since the UN approved its last penalties in 2017.

The Biden administration has shown increasing frustration with China, which has long been North Korea's most important benefactor. And the stakes are rising because the U.S. and its allies believe Kim's regime is preparing to detonate a nuclear bomb for the first time in five years. s

"They are breaking multiple Security Council resolutions," Linda Thoma-Greenfield, the U.S. ambassador to the UN, said in an interview on MSNBC on Thursday. "But most recently, China has not joined us in condemning these actions and our efforts to add more sanctions onto the ones that we already have on board."

The U.S. is expected to make another run at getting support for fresh measures against North Korea at a Security Council meeting scheduled for Friday afternoon in New York. Beijing and Moscow have resisted U.S.-led efforts to expand sanctions in recent years, arguing that Kim deserves relief for gestures he made before his unprecedented -- but ultimately unsuccessful -- summits with former President Donald Trump.

More recently, U.S. President Joe Biden has sanctioned Russia and sought to isolate its leader Vladimir Putin to halt its war in Ukraine. The administration has also warned Chinese leader Xi Jinping that he risks secondary sanctions if he helps Moscow, even as Washington and Beijing clash over everything from Taiwan to microchips.

Those disputes have given Kim a freer hand to expand his nuclear program and build a more credible deterrent to prevent any U.S. strike against the regime. North Korea's tests have demonstrated a wide array of new missiles and launching platforms that appear intended to evade detection and interception by the U.S..

"North Korea knows the recent provocations won't trigger any new UN resolutions," said Maiko Takeuchi, a former member of a UN Security Panel of Experts set up to monitor sanctions on North Korea. If current sanctions were strictly implemented, that would also "seriously damage the regime's activity and economy," she said.

The sanctions regime, which, among other things, includes a cap on fuel imports and limits on foreign income, has shown cracks. North Korea was on track to exceed its 500,000-barrel cap of annual imports this year, a Panel of Experts report released in September said.

In addition, an oil pipeline between Dandong, China, and Sinuiju, North Korea, that was exempted from sanctions could be supplying more than 3.7 million barrels of oil each year, according to a report from specialists David von Hippel and Peter Hayes.

Kim has also found ways to evade sanctions through cybercrimes and cryptocurrency theft. Investigators from the U.S. and UN have said his regime has already taken in hundreds of millions of dollars in assets through online schemes, and is poised to rake in even more.

The North Korean leader has repeatedly rebuffed U.S. overtures to return to talks, reiterating in September that he would "never give up nuclear arms or denuclearize first." Instead, he has rebuilt once-frayed ties with China and Russia -- whom both wield vetoes on the Security Council.

Xi has recently reaffirmed his desire to maintain "strategic" talks with Kim. And the Biden administration has accused North Korea of covertly supplying Russia with artillery shells for use in the Ukraine invasion, something North Korea has denied.

Without necessary support for UN sanctions, the U.S. and South Korea have sought to deter North Korea from any more aggressive moves, jointly warning it that using a nuclear weapon against them would "result in the end of the Kim regime." They also extended allied air force exercises in the region.

One indication of Chinese support for additional sanctions will be its response to any North Korean nuclear test, especially after Xi told visiting German Chancellor Olaf Scholz on Friday that the international community must "reject the use or threat of the use of nuclear weapons." China denounced North Korea's last test in September 2017, expressing "firm opposition to and strong condemnation" of it.

North Korea may be banking that China won't be so critical the next time. Kim's actions indicate a broader shift away from the country's long-term goal of normalizing ties with Washington as a buffer against Beijing and Moscow, said Rachel Minyoung Lee, who worked as an analyst for the CIA's Open Source Enterprise for almost two decades.

"The true import of this policy shift extends beyond just North Korea's pivot to China and Russia," Lee wrote in a commentary published on the 38 North website. "It signals a more fundamental transformation in Pyongyang's position on relations with Washington."