By Chun Han Wong in Beijing and Jonathan Cheng in Seoul

New international sanctions against North Korea's economy signaled an emerging consensus between China and the U.S. on the urgency of halting Pyongyang's advancing nuclear program despite doubts over their efficacy.

The United Nations Security Council sanctions resolution, adopted on Wednesday, aims to cut North Korea's annual exports by an estimated $800 million--roughly one quarter of its total--by imposing a cap on its coal exports to China.

But months of wrangling over the sanctions yielded an agreement that, on its own, many experts say are unlikely to persuade North Korean leader Kim Jong Un abandon his pursuit of becoming a world-recognized nuclear power. Progress on this front depends much on how rigorously China enforces the coal cap, and whether Beijing, Washington and other governments follow up with more diplomatic efforts.

While agreeing to tougher sanctions is a necessary step, China and the U.S. must continue to work together to create a "conducive political environment" for peacefully ending North Korea's nuclear ambitions, which includes providing Pyongyang assurances for its national security, said Yang Xiyu, a Korean affairs expert and senior fellow at the China Institute of International Studies, a Chinese Foreign Ministry-affiliated think tank.

North Korea's state-run news agency hasn't commented on the new resolutions.

The Obama administration considers North Korea's pursuit of a functional warhead that can reach American shores a major threat. It will be one of the most urgent national security issues for President-elect Donald Trump when he takes office in January. On the campaign trail, Mr. Trump hinted he was willing to negotiate a rapprochement directly with Mr. Kim, breaking from a past emphasis on multilateral talks with the dictator.

China, North Korea's closest ally, has in the past resisted adopting tough economic sanctions on Pyongyang, concerned most about the stability of a poor country on its border. But in adopting the sanctions, Beijing seemed to calculate the new penalties won't destabilize North Korea. China said it was reacting to a situation it said had grown "dire" following a series of nuclear tests by Pyongyang.

Experts say Beijing's decision to target a key source of Pyongyang's income is aimed at admonishing North Korean leader Mr. Kim for his persistence in pursuing nuclear weapons without jeopardizing his regime's survival.

China, the world's largest coal producer and consumer, is the only importer of North Korean coal, according toU.S. officials. The imports dipped for a few months after the U.N. passed a March resolution to curb North Korean exports of coal, iron and iron ore, but have recovered in recent months.

In the first 10 months of this year, China bought 18.5 million tons of North Korean coal worth roughly $877 million, compared with 16.4 million tons worth $902 million in the corresponding period a year earlier, according to Chinese customs data.

The U.N. resolution would cap North Korea's coal exports at about $400 million, or 7.5 million metric tons, a year.

Chinese imports of North Korean coal reached a monthly record of nearly 2.5 million tons in August, though Beijing has denied violating the March resolution, citing exceptions made for trade that is deemed necessary for sustaining normal livelihoods in North Korea.

But some experts see such leniency as a sign that Beijing won't enforce the sanctions, which depend on reliable tradedata from China. They also point to oil data as a case in point. Since early 2014, Chinese official trade data have omitted statistics on Beijing's exports of crude oil to North Korea. Oil shipments from China are critical to keep the decrepit North Korean economy functioning. The North has little oil supply of its own.

Most observers agree that properly enforced sanctions would significantly hurt North Korea's economy. "North Korea will be hard-pressed and strapped for cash," said Lee Jung-hoon, South Korea's ambassador for North Korean human rights.

What effect there is beyond that is unclear. South Korea's intelligence agency estimates North Korea spent around $200 million on two nuclear tests and multiple missile launches this year, leaving it room to preserve the program while tightening elsewhere. Still, some people viewed the resolution as potentially effective.

George Lopez, a professor at University of Notre Dame and aformer member of the U.N. Panel of Experts for monitoring sanctions on North Korea, said the new sanctions are tougher than North Korea expected. He said they would complicate North Korea's weapons-program procurement, delay the program by several months and probably change the Pyongyang's calculus on whether and when to conduct another nuclear test.

"If they were thinking of greeting Mr. Trump with a new test around inauguration, this ups the ante on that," Mr. Lopez said. "I don't think they expected this kind of draconian incursion into their real money and this kind of strict monitoring."

Some Chinese experts, however, cautioned against pinning too much hopes on the latest measures.

"It's doubtful whether the new resolution can completely cut off the funding needed for North Korea's nuclear and ballistic missile programs, " said Zhang Liangui, a North Korea expert at the Central Party School, an elite Chinese training academy. "North Korea has plenty of means for securing funds, and it's hard to separate military from civilian uses under such a regime."

Alastair Gale in Tokyo and

Kersten Zhang

in Beijing contributed to this article.

Write to Chun Han Wong at chunhan.wong@wsj.com and Jonathan Cheng at jonathan.cheng@wsj.com

(END) Dow Jones Newswires

December 01, 2016 01:03 ET (06:03 GMT)

Copyright (c) 2016 Dow Jones & Company, Inc.