President Trump and his secretary of state, Mike Pompeo, voiced optimism on Thursday about efforts to reinstate a canceled summit meeting with Kim Jong-un of North Korea. But Mr. Kim also welcomed a top Russian official to Pyongyang, offering a reminder that competing powers could still buffet the White House’s effort to salvage the meeting.
Mr. Pompeo, who met over two days with a senior emissary of Mr. Kim in New York, said afterward that he was “confident we are moving in the right direction.”
It would be “nothing short of tragic to let this opportunity go to waste,” Mr. Pompeo said after two and a half hours of discussions with Kim Yong-chol, the former North Korean intelligence chief and top nuclear arms negotiator. “If these talks are successful, they will truly be historic.”
The diplomacy is expected to continue on Friday in Washington, where Mr. Trump said he expected to receive a letter from the North Korean leader, hand-delivered by his envoys.
Still, as the pace of diplomacy accelerated in the United States, Kim Jong-un was conducting his own outreach to a major American adversary at home. Foreign Minister Sergey V. Lavrov became the first senior Russian official to meet with the young North Korean leader, extending an invitation from President Vladimir V. Putin for Mr. Kim to visit Moscow.
Mr. Lavrov called for the lifting of sanctions on North Korea — the centerpiece of Mr. Trump’s strategy for drawing the North to the bargaining table — and endorsed moves toward reconciliation on the Korean Peninsula.
“It’s absolutely clear that when starting a discussion about solving the nuclear problem and other problems on the Korean Peninsula, we proceed from the fact that the decision cannot be complete while sanctions are in place,” Mr. Lavrov said.
White House officials declined to address the implications of Mr. Kim’s meeting with Mr. Lavrov. But Mr. Trump expressed suspicion recently about a meeting between Mr. Kim and another American adversary, President Xi Jinping of China, which he said came just before a noticeable change in North Korea’s tone toward the United States.
Though Russia exerts less influence over the North than China, it does share an 11-mile border. Analysts said Moscow has subtly undermined the American-led effort to squeeze North Korea economically by allowing its ships to use Russian ports.
“The hidden story of what’s been going on with North Korea over the last year is that Russia has always been a safety valve for them,” said Evan S. Medeiros, who served as President Barack Obama’s top Asia adviser. “It’s one more way that Trump’s maximum pressure campaign gets diluted.”
In New York, Mr. Pompeo cited “real progress” toward rescheduling a summit meeting between Mr. Kim and Mr. Trump that was set for June 12 in Singapore, before the president canceled it last week.
Mr. Pompeo maintained that the United States would continue to demand a fully verifiable and irreversible denuclearization of the Korean Peninsula. But he acknowledged that significant challenges remained and predicted more “tough moments and difficult times” as the two sides negotiate.
For his part, Mr. Trump said it was unclear whether the show of tenuous détente would be enough to strike a deal to hold the summit meeting. But he told reporters that the negotiations — which both sides hope will end decades of enmity and suspicion — were “in good hands.”
The meeting set for Friday came as a surprise even to some on Mr. Trump’s staff, and he offered few details when he announced it.
It would be a rare visit, similar to one made to Washington in 2000 by Vice Marshal Jo Myong-rok, who was then North Korea’s second-most-powerful official. Mr. Jo met President Bill Clinton and delivered a letter from North Korea’s leader at the time, Kim Jong-il.
Mr. Trump’s decision to personally meet the North Korean envoy displayed his eagerness to be at the center of the action for the high-stakes talks.
A senior State Department official told reporters on Wednesday night that it would be natural for the North Korean delegation to pass communications through Mr. Pompeo, who would then deliver it to the president. The official, who spoke on the condition of anonymity, said that he would be surprised if the envoys personally delivered a letter to the president.
Michael Green, a former senior Asia adviser to President George W. Bush, said the flurry of diplomatic activity had already led South Korea, Russia and China to propose, consider or undertake a softening of sanctions.
“North Korea’s goal is to defuse sanctions, and it’s already working,” Mr. Green said. “There’s nothing that the North Koreans have put on the table that suggests any serious intent to denuclearize.”
American and North Korean envoys have also been meeting in Panmunjom, in the Demilitarized Zone between North and South Korea, and another set of officials has held talks in Singapore to hash out the logistics of putting the June 12 summit meeting back on.
The blizzard of meetings is a breathtaking change from the bellicose language the two sides lobbed at each other for much of last year, with Mr. Trump threatening to unleash “fire and fury” against North Korea if it endangered the United States.
But the two sides still remain far apart. The Trump administration has largely insisted that North Korea commit itself to a rapid and complete unwinding of its nuclear program, although the president recently opened the door to a phased dismantling.
President Moon Jae-in of South Korea, who served as an early mediator between Washington and Pyongyang, is known to favor a step-by-step process that would lift some sanctions against North Korea in exchange for verifiable steps to stop or reverse its weapons programs. North Korea is also believed to favor such an approach.
On Thursday, Mr. Pompeo tried to reassure both Japan and South Korea, whose leaders have been deeply uneasy with Mr. Trump’s surprise announcements and unpredictability. They also have been rattled by reports that the American president had ordered the Pentagon to prepare options for drawing down United States troops in South Korea.
Mr. Pompeo said there was “no daylight” among the United States, Japan and South Korea on how to resolve the standoff with North Korea. He also said the United States had heard and understood the concerns of its two allies in the region.
Sung-Yoon Lee, a professor at the Fletcher School of Law and Diplomacy at Tufts University, said he expected North Korea to follow its consistent script of calling for further dialogue and regular in-person meetings — but no real efforts to surrender its weapons programs.
Mr. Lee, a North Korea scholar, said in an email that he viewed it as “another example of North Korea being North Korea — how the regime has mastered the weaponization of its own weirdness.”
Mr. Lavrov’s visit to Pyongyang was the first by the Russian foreign minister to North Korea in nearly a decade, and seemed intended to reassert Moscow’s longstanding interests in the Koreas on the eve of the possible summit meeting between Mr. Kim and Mr. Trump.
Before leaving Moscow, Mr. Lavrov had said Russia was not involved in talks over the United States-North Korea summit meeting. But Moscow was a party in previous negotiations on the nuclear question, and it has offered itself as a possible mediator between the North and South.
In addition, Mr. Putin has made a habit of prodding for gaps and weaknesses in American foreign policy that he can exploit. His spokesman, Dmitri S. Peskov, said it was premature to discuss the timing of any such visit by Mr. Kim to the Russian capital.
Russia earns an estimated $120 million a year by seizing the wages of construction workers employed in Russia, along its border with the North, according to the Database Center for North Korean Human Rights, a group in Seoul.