WASHINGTON - China's increasingly icy posture is thrusting Russia forward as North Korea's preferred diplomatic partner, forcing the Trump administration to turn to Moscow for help in isolating the rogue, nuclear-armed nation.

Beijing's close ties to Pyongyang have been strained since leader Kim Jong Un ordered the 2013 execution of his uncle who had been the countries’ chief liaison. Since then, the allies once said to be as “close as lips and teeth” have moved further apart over China's adoption of U.N. sanctions designed to starve North Korea of revenue for its nuclear and missile programs.

But China isn’t North Korea’s only traditionally friendly neighbor. And for the United States, Russia's increased importance comes at an uncomfortable time. The State Department on Friday warned countries and companies around the world they risk being blacklisted if they do business with dozens of Russian firms. Investigations also continue into allegations Russia interfered in last year's U.S. presidential election.

U.S. special representative for North Korea policy U.S. special representative for North Korea policy Joseph Yun answers questions from reporters, April 25, 2017, in Tokyo. U.S. special representative for North Korea policy Joseph Yun answers questions from reporters, April 25, 2017, in Tokyo.

“Russia could play a useful diplomatic role,” Joseph Yun, the U.S. envoy to North Korea, said in an Associated Press interview. “If Russia delivers a unified message with the U.S., China, South Korea and Japan that the U.S. is not interested in regime change but rather we want to resolve the WMD issue, they can help better than anyone else to convince them of that.”

Yun said he and Secretary of State Rex Tillerson want Moscow to support the international pressure campaign against North Korea by implementing U.N sanctions, and to urge the isolated, often inscrutable government to engage in diplomatic efforts. Washington also wants to prevent transfers of weapons technology, amid disputed assessments that North Korea may have acquired a high-performance missile engine through illicit networks in Russia or Ukraine.

CIA Director Mike Pompeo speaks during the Foundat CIA Director Mike Pompeo speaks during the Foundation for Defense of Democracies National Security Summit in Washington, Oct. 19, 2017. CIA Director Mike Pompeo speaks during the Foundation for Defense of Democracies National Security Summit in Washington, Oct. 19, 2017.

Like China, Russia has urged a peaceful resolution as Kim and President Donald Trump trade personal insults and threats of war. CIA Director Mike Pompeo recently said Pyongyang is only months away from a nuclear-tipped missile that could strike the United States, a timeline that has raised American alarm and escalated fears of a resumption of the 1950-53 Korean War.

In the meantime, Russia has cast itself as a potential go-between.

Choe Son-hui, director-general of the North America bureau at North Korea’s Foreign Ministry, has visited Moscow twice in the past month — most recently to attend a nonproliferation conference where she spoke on a panel alongside a nongovernmental American expert and a senior Russian diplomat. Russian Foreign Minister Sergey Lavrov opened the event. Choe also met with Russia’s ambassador to North Korea in Pyongyang last month.

“They seem to be communicating, which is good,” Yun said.

Suzanne DiMaggio, the American expert who sat on the panel with Choe, said: “If you look at all the major players in this crisis, the only one with a working relationship with Pyongyang is Moscow.”

“Moscow appears to be positioning itself to play an intermediary role,” she said. “Whether that’s looked upon favorably by the U.S. administration remains to be seen.”

Choe told the conference that North Korea wants to develop its nuclear and missile capabilities until they reach a “balance of power” with the United States. But DiMaggio said it was also apparent the North Koreans want to keep channels of communication open.

That’s where Russia could come in. It has participated in past nuclear diplomacy and was among six nations involved in aid-for-disarmament talks that collapsed almost a decade ago.

While the North’s ties with China have slumped, relations with Russia remain comparatively smooth. Although Russia, too, has endorsed U.N. sanctions, it maintains fraternal ties with North Korea dating back to when the Soviet Union trained and supported Kim Il Sung, who later founded North Korea. The U.S.S.R. then provided economic and military assistance through the Cold War.

Russia’s influence goes only so far, however. Its commerce with the North is minimal compared to China, which accounts for 90 percent of North Korea's external trade and has agreed to cutting off crucial imports of coal, iron ore and textiles. Such actions prompted rare North Korean criticism of China in state media this year.

China doesn’t want war. Nor does Russia. And Trump’s repeated threats of military action have put him at odds with Russian President Vladimir Putin, who advocates dialogue. Last week, Putin warned: “North Korea should not be backed into a corner.”

President Donald Trump waits in the Oval Office of President Donald Trump waits in the Oval Office of the White House, Oct. 24, 2017. President Donald Trump waits in the Oval Office of the White House, Oct. 24, 2017.

Trump responded this week by criticizing Russia’s level of cooperation, saying it has hurt U.S. efforts while China had helped. With improved U.S.-Russian relations, Trump told Fox Business Network, “I think that North Korean situation would be easier settled.”

Putin’s spokesman told the AP that Putin sees things similarly. Better ties could help “crises including North Korea,” Dmitry Peskov said.

So far, Moscow hasn’t threatened to stymie coordinated efforts over separate gripes with Washington. But as relations sours — involving even staff eliminations at each other's diplomatic offices — it’s unclear if they can continue compartmentalizing their cooperation. One bone of contention concerns the North Korean laborers in Russia that send significant money back to their government.

A larger question is how Russia might bridge the U.S.-North Korean divide. Both reject Chinese and Russian proposals for North Korea to stop nuclear and missile tests if the U.S. and South Korea abandon joint military exercises.

National Security Adviser H.R. McMaster attends a National Security Adviser H.R. McMaster attends a ceremony in the East Room of the White House in Washington, Oct. 23, 2017. National Security Adviser H.R. McMaster attends a ceremony in the East Room of the White House in Washington, Oct. 23, 2017.

H.R. McMaster, Trump’s national security adviser, also recently addressed Russia’s importance with North Korea, saying it maintained “considerable influence.” At a security forum last week, he urged Moscow to help “convince Kim Jong Un and his regime to move toward denuclearization of the peninsula as really a last chance to avoid severe consequences.”

Andrei Lankov, a veteran Russian scholar of Korean policy at Kookmin University in Seoul, said Moscow wants to avoid a conflict and reinforce its prestige as an international player.

“Russia is a status quo power when it comes to the Koreas, and the war is its worst nightmare,” he said.