UNITED NATIONS — The United Nations Security Council placed new sanctions on North Korea on Friday that significantly choke off fuel supplies and order North Koreans working overseas to return home, in what may prove the last test of whether any amount of economic pressure can force the isolated country to reverse course on its nuclear weapons program.
The sanctions, proposed by the United States and adopted by a vote of 15 to 0, were the third imposed this year, in an escalating effort to force the North into negotiations. China and Russia joined in the vote, in a striking display of unity, but only after the Trump administration agreed to soften a couple of the provisions.
Under the new sanctions, the amount of refined petroleum North Korea can import each year will be cut by 89 percent, exacerbating fuel shortages. Roughly 100,000 North Korean laborers who work in other countries, a critical source of hard currency, will be expelled within two years. Nations will be urged to inspect all North Korean shipping and halt ship-to-ship transfers of fuel, which the North has used to evade sanctions.
But the resolution does not permit countries to hail or board North Korean ships in international waters, which the Trump administration proposed in September. That would be the most draconian measure, because it would enable the United States Navy and its Pacific allies to create a cordon around the country, though Pentagon officials say it would risk setting off a firefight between North Korea and foreign navies.
The new sanctions are the toughest ever, but so were the last two rounds: In August, the Security Council blocked North Korean exports of coal, iron, iron ore, lead, lead ore and seafood, and in September, it blocked textile exports, curbed oil imports and called for inspections of ships that have visited the North’s ports.
Experts, and even the White House, agree that the United States is running out of sanctions options. The C.I.A. assessment is that no amount of economic sanctions will force the North Korean leader, Kim Jong-un, to give up his country’s nuclear program.
“President Trump has used just about every lever you can use, short of starving the people of North Korea to death, to change their behavior,” the White House homeland security adviser, Thomas P. Bossert, said Tuesday. “And so we don’t have a lot of room left here to apply pressure to change their behavior.”
The vote came just four days after the United States charged that the North was responsible for the “Wannacry” cyberattack that crippled computers around the world in May, and nearly a month after the country launched a new intercontinental missile that appears capable of reaching any city in the United States.
The United States, which has led the sanctions effort at the Security Council, drafted the latest round in consultation with other members, notably China, which historically has been reluctant to impose them for fear of destabilizing North Korea, its neighbor.
There were some last-minute changes in the final version of the resolution, partly to satisfy Russian complaints. The changes included doubling the deadline for the return of North Korean workers to 24 months from 12 months.
Russia’s deputy ambassador, Vladimir Safronkov, who attended the Security Council vote, made a point of complaining about negotiations over the resolution, in which he said Russia had not been adequately consulted.
Still, Russia went along with the new measures — though American officials have charged that in recent months the Russians have secretly opened new links to the North, including internet connections that give the country an alternative to communicating primarily through China.
The unanimous decision was a diplomatic achievement for the Trump administration, only a day after most members of the United Nations General Assembly, brushing aside President Trump’s threats of retaliation, condemned the United States’ new recognition of Jerusalem as Israel’s capital.
Nikki R. Haley, the American ambassador, thanked the other Council members — especially China — for coming together on the resolution and said further North Korean defiance would “invite further punishment and isolation.”
Ms. Haley called North Korea’s intercontinental ballistic missile test last month “another attempt by the Kim regime to masquerade as a great power while their people starve and their soldiers defect.”
China’s deputy ambassador, Wu Haitao, said the latest measures reflected “the unanimous position of the international community” and he urged North Korea to “refrain from conducting any further nuclear and missile tests.”
But he also emphasized China’s longstanding position that all antagonists in the dispute needed to de-escalate and find ways to resume a dialogue, asserting that there was “no military option for settling the nuclear issue” on the Korean Peninsula.
Speaking to reporters before the meeting, Matthew Rycroft, the British ambassador, said the unity of Council members on North Korea showed they were “seeing the bigger interests we all have.”
Asked if the new measures would make life even harder for ordinary North Koreans, Mr. Rycroft blamed their government, saying it “uses every cent, every penny that it can on its nuclear program and its intercontinental ballistic missile program and nothing at all on the welfare of the poor people of North Korea.”
Under Mr. Kim, a grandson of the country’s founder, Kim Il-sung, the impoverished country of 25 million has exalted nuclear weapons and threatened to use them against the United States, its No. 1 perceived enemy since an armistice halted the Korean War in 1953.
The increased sanctions are part of a strategy that, so far, has relied more on coercive diplomacy than on military action, though there is a long history of American efforts to sabotage North Korea’s missile and nuclear programs.
But inside the administration, there are clear differences of opinion over how long Mr. Trump can, or will, tolerate a growing threat from North Korea without resorting to some kind of military force.
While diplomacy backed by sanctions is the clear preference of Secretary of State Rex W. Tillerson and Defense Secretary Jim Mattis, others inside the administration say there is little time left for the sanctions to stop the North from achieving the ability to strike the United States with a nuclear weapon.
Yet to prove effective, sanctions must be strictly enforced and require many months or several years to take effect. Even then, there is no guarantee: Despite all the sanctions heaped on North Korea in recent years, its economy grew 3.9 percent last year, by most estimates.
Mr. Trump’s national security adviser, Lt. Gen. H. R. McMaster, has said in recent weeks, “There isn’t much time left.” That would suggest that even the new sanctions may not bite in time to change the calculus of the North Korean leadership. The fear in Washington, among those looking for a diplomatic solution, is that Mr. Trump will decide on some kind of pre-emptive strike, betting that the North will stop short of major retaliation.
The North Koreans have conducted six nuclear tests and have demonstrated major progress with their missiles even though the United Nations has prohibited them.
Experts on North Korea said the new measures had the potential to dissuade Mr. Kim from further escalating tensions with more tests, but they were cautious about predicting his behavior.
“If the international community, including countries like China and Russia, implements these measures fully, faithfully and quickly, it will apply an unprecedented and irresistible level of pressure on the North Korean regime,” said Evans J. R. Revere, a former senior State Department diplomat for East Asia.
If that happens, he said, it would force North Korea “to make a choice” between defiance and negotiations.
Others were more skeptical.
“If we are playing the long game, the accumulation of sanctions could eventually force North Korea to come to the table and negotiate,” Sue Mi Terry, a former C.I.A. analyst now at the Center for Strategic and International Studies, said in an email.
However, she said it was doubtful that the move would persuade Mr. Kim “to give up his nuclear arsenal or even discuss a freeze” in 2018.
Jae H. Ku, director of the U.S.-Korea Institute at the Johns Hopkins School of Advanced International Studies, said he feared that North Korea would “continue to weather the pressure” of sanctions.
“The upshot,” he said, “would be the Trump administration admitting that maximum pressure to gain a diplomatic solution is a lost cause.”