UNITED NATIONS — In an effort to tighten sanctions that largely failed to throttle North Korea’s nuclear program, the United Nations Security Council on Wednesday imposed a cap on coal exports, the country’s chief source of hard currency.
The new penalties — adopted unanimously by the Council, including China — came as North Korea advances toward its goal of building a functional nuclear warhead. That presents a stark national security challenge to the incoming administration of President-elect Donald J. Trump, who called North Korea’s leader, Kim Jong-un, “a maniac” during the campaign, but has said nothing about how to contain Mr. Kim’s nuclear ambitions.
As with the originỎnal set of sanctions, which the Security Council adopted in March, the key to enforcing these new penalties remains in the hands of China, North Korea’s principal patron and coal customer.
The new restrictions on North Korean coal were relatively easy for Beijing to approve. They serve the purpose of expressing China’s displeasure with Mr. Kim’s agenda, yet they fall short of inflicting crippling pain on North Korea.
China seems to have judged that reducing the coal imports will not upend the North Korean economy and cause social unrest and flows of refugees into China, an outcome it most fears.
On Wednesday, China’s permanent representative to the United Nations, Liu Jieyi, called on North Korea to halt its nuclear tests, saying they undermine regional stability and Beijing’s “strategic interests.” He said the resolution demonstrated “the uniform stance of the international community.”
Samantha Power, the American ambassador to the United Nations, said Wednesday that “the United States recognizes China in working closely with us.” Negotiations lasted for three months, since Pyongyang’s fifth and latest nuclear test in September.
The original sanctions — which the United States at the time hailed as “comprehensive” — had sought to limit coal exports, unless it was for what the measure called “livelihood” reasons. In spite of the sanctions, exports to China increased.
American officials conceded this week that there was some “vagueness” in the original measure. The new resolution aims to shave $700 million from North Korea’s coal revenues. The resolution says North Korea can sell no more than 7.5 million metric tons of coal a year, or bring in no more than $400 million in sales, whichever comes first.
It also requires countries to tell the United Nations how much North Korean coal they are buying and expands the list of banned items for import by North Korea, including luxury goods like bone china worth more than $100 as well as equipment with dual-use purposes.
The measure also urges countries to allow North Korean diplomatic missions around the world to have only one bank account. That, the United States says, is intended to limit the country’s penchant for using its envoys and embassies to further its nuclear program.
How successful the new measures will be, of course, depends on the willingness of countries to abide by them.
The United Nations secretary general, Ban Ki-moon, called the measures the “toughest” sanctions imposed by the Council. But he warned that the passage alone would be insufficient. “It is incumbent on all member states of the United Nations to make every effort to ensure that these sanctions are fully implemented,” he said.
The bigger uncertainty is what posture Mr. Trump will take toward North Korea and Mr. Kim — and, by extension, toward Beijing.
“If you look at North Korea, this guy, I mean, he’s like a maniac, O.K.?” Mr. Trump said at a campaign rally in January. He went on to say that “he really does have missiles, and he really does have nukes.” Since then, Mr. Trump and his transition team are likely to have been briefed on the nature and scope of North Korea’s nuclear arsenal.
American officials have warned for months that the North’s nuclear capabilities have increased sharply. Its missile and nuclear tests, the most recent in September, have accelerated, despite the imposition of sanctions in March.
The Security Council measures adopted on Wednesday are a response to the Kim government’s fifth and largest nuclear test. The revised sanctions are aimed at cutting into North Korea’s ability to profit from coal exports and to tighten the noose around individuals and companies involved in its nuclear program. The measure expands the list of people subject to asset freezes and travel bans; they include some envoys to countries like Egypt and Sudan.
American officials said the new sanctions would also clarify that the “livelihood” exemption applies to North Korean citizens, and cannot be used to protect the livelihoods of Chinese importers.
Publicly, China has defended its coal imports since the sanctions earlier this year. Even if statistics showed increased imports, the trade was legal under the livelihood exemption, the Foreign Ministry said.
Chinese analysts point to conditions flourishing in the North Korean capital, Pyongyang, and say rudimentary market trading in rural areas is keeping much of the population afloat.
And even though some Chinese steel makers in northern China value North Korea’s high-grade coal, the new curbs would have relatively little impact on China’s industrial output, said Deng Shun, a coal market analyst with Success Futures, a trading company in Guangzhou.