Japan is apparently stumped over how to deal with North Korea, which carried out its sixth nuclear test Sunday in defiance of international warnings, political experts say.

Following the test, Pyongyang’s most powerful to date, Japan agreed with the United States and South Korea to put more pressure on the country, following the same pattern used to deal with past provocations by North Korea.

The experts, however, say North Korean leader Kim Jong Un will not abandon his policy of pursuing weapons of mass destruction unless the continuation of his regime is accepted by U.S. President Donald Trump.

A ray of hope is that China, with its influence over Pyongyang, will join hands with Prime Minister Shinzo Abe and Trump to bolster pressure on North Korea, which went ahead with the nuclear test despite strong opposition from Beijing, the experts say.

On Sunday, North Korea said through its official media that it successfully tested an advanced hydrogen bomb and now has the ability to adjust the power of a warhead as it pleases in accordance with the target.

Pyongyang’s last nuclear test was held in September 2016. Since then, it has continued to test missiles, including two intercontinental ballistic missiles fired into the Sea of Japan in July, and one that flew over Japan into the Pacific Ocean late last month.

Abe quickly condemned Sunday’s test and called for other members of the United Nations to “show a strong will to protect world peace.”

Foreign Minister Taro Kono also met with U.S. Ambassador to Japan William Hagerty, and held telephone talks with South Korean Foreign Minister Kang Kyung Wha.

By steadily implementing existing U.N. Security Council sanctions resolutions against Pyongyang and adopting new, stricter penalties, Tokyo, Washington and Seoul will try to achieve “denuclearization” in North Korea, Kono told reporters.

But Stephen Nagy, a senior associate professor of politics at International Christian University in western Tokyo, said sanctions won’t be effective in curbing North Korea’s missile and nuclear ambitions.

“Pyongyang’s central interest in regime survival will dictate that the North will continue to press forward in missile development and the refinement of its nuclear weapons,” Nagy said.

“This national goal is in complete contrast to the U.S. administration and all other countries in the region, meaning tensions will continue to rise, distrust will deepen and both sides will continue to stress that each country is an existential threat to each other,” he said.

Moreover, Nagy pointed out that the North Korean leader has “strategically” pushed his policies, while understanding the United States under Trump is “a rudderless ship” that is “incapable of a sustained, strategic approach to dealing with the North.”

“There is very little the United States and Japan can do to further tighten the noose around the North Korean neck,” Nagy said.

Other diplomatic analysts echo the view, saying that if Abe wants to boost the efficacy of U.N. sanctions on Pyongyang, he should persuade China to act in concert.

Beijing, which accounts for around 90 percent of North Korea’s total foreign trade, is the chair of the long-stalled six-party talks involving the two Koreas, China, Japan, Russia and the United States, aimed at denuclearizing the Korean Peninsula.

Mitoji Yabunaka, a former vice minister at Japan’s Foreign Ministry, said on a TV program that Beijing has been concerned that North Korea’s possession of nuclear weapons could prompt other neighboring countries such as South Korea to acquire nuclear arms.

Although China had stressed the importance of seeking a diplomatic solution to reduce the tensions, Sunday’s nuclear test apparently angered China and prompted it to rap North Korea in stronger terms.

Calling on North Korea to avoid taking any “wrong” action that would aggravate the status quo, China’s Foreign Ministry said in a statement that Beijing is “unswervingly” committed to cooperating with the international community to safeguard the peace and stability of the Korean Peninsula.

Japan’s Kono said, “China issued a statement that includes very strong words that it has not used before,” adding, “I think China has become inclined to put pressure on North Korea.”

The nuclear test came as Chinese President Xi Jinping hosts a summit of emerging economies in his country — an important diplomatic opportunity to cast himself as an influential global leader ahead of next month’s twice-a-decade congress of the Communist Party.

Trump said in a Twitter post, “North Korea is a rogue nation which has become a great threat and embarrassment to China.”

A Japanese foreign ministry official said North Korea has “brought shame on” Beijing and Xi might take harsh measures against Pyongyang down the road.

But Hiroko Imamura, a professor at the University of Toyama, disagreed, noting China has been recently “unable to exert its influence on North Korea as strongly as Japan, the United States and South Korea expect.”

Even if Beijing works hard, it will be difficult to stop the inflow of funds into North Korea and prevent Kim from developing ballistic missiles and nuclear weapons, Imamura said.

Despite the predicament, many security pundits believe a U.S. military strike on Pyongyang is unlikely because Washington’s allies — Seoul and Tokyo — will pay too high a price.