An unscheduled Russian military VIP plane touched down in Pyongyang this week, days after North Korean leader Kim Jong Un made a rare trip to his neighbor for talks the US said likely focused on arms transfers.

Tracking data from FlightRadar24 shows the Russian Air Force Ilyushin IL-62M flying from Moscow to Pyongyang, arriving on Tuesday morning. The tail number on the plane indicates it was the same aircraft Russia sent to North Korea in August, just days after Defense Minister Sergei Shoigu traveled to Pyongyang and was guided by Kim through a collection of his country’s latest weaponry.

Data from FlightRadar24 also indicates the plane returned to Russia on Thursday after having been on the ground in North Korea for about two days. North Korean state media has made no mention of the plane and the Russian Defense Ministry did not respond to a request for comment sent by email.

Specialist service NK News, which spotted the plane’s arrival, said the silence surrounding the flight could indicate there were military officials on board for talks on weapons or technology transfers. About a day after the plane departed Pyongyang, Russia’s official Tass news agency reported that North Korea’s Minister of External Economic Relations Yun Jong Ho had arrived in Moscow for a working visit.

North Korea has had almost no international air traffic since it closed its borders at the start of the pandemic in early 2020. The arrival of two flights in the space of less than two months highlights cooperation between the two countries, which have drawn closer as the US and its partners tried to isolate them with international sanctions.

“It seems that Russia has rediscovered the strategic value of North Korea against the backdrop of North Korea’s support in the war and the formation of the US-South Korea-Japan trilateral alliance,” said Jeh Sung-Hoon, head of the department of Russian Studies at Hankuk University of Foreign Studies.

“Since the interests of both countries are aligned, North Korea-Russia cooperation should move forward quickly,” Jeh said.

Kim spent about a week in Russia this month where he held a summit with Vladimir Putin at Russia’s Vostochny Cosmodrome space center. He received pledges from the president of assistance in building satellites and firing them off on Russian rockets.

The US for months has accused Kim of providing arms and ammunition to aid Putin’s war in Ukraine, with a Pentagon spokeswoman saying it’s a sign of desperation for the Kremlin to be turning to North Korea for help.

The US has said while weapons such as artillery shells and rockets will help Russia, they aren’t likely to alter the battlefield. The sales could also provide North Korea with a new stream of revenue for an economy isolated from much of world trade.

During his visit to Russia, Kim toured military facilities including plants that make fighter jets.

US Secretary of State Antony Blinken said the visit highlighted an “increasingly dangerous” two-way street between Russia and North Korea. In a speech Monday in Washington, he said there’s a situation playing out with “Russia desperate to find equipment, supplies, technology for its ongoing aggression against Ukraine, but also a DPRK that is looking for help to strengthen and advance its own missile programs.”

North Korea might be looking at technology transfers of dual-use materials that could be delivered under the guise of helping its civilian space and nuclear programs in accordance with international norms. But those items could also be used to further North Korea’s ability to build missiles and nuclear bombs — in violation of United Nations Security Council resolutions.

Read: Kim Makes ‘Exponential’ Nuclear Growth Supreme Law to Defy US

The next high-level official visit between the two is expected in October, when Russian Foreign Minister Sergey Lavrov is set to make a visit to Pyongyang.

There had not been any official envoys since early 2020 when North Korea shut its borders due to the pandemic until July. That’s when a delegation led by Shoigu and another from China led by Li Hongzhong, who sits on the Communist Party of China’s 24-member Politburo, traveled to North Korea to attend celebrations marking the 70th anniversary of the end of fighting in the 1950-1953 Korean War.

“To what degree Russia is willing to circumvent UN Security Council resolutions is another big question,” said Jaewoo Shin, an analyst at the Open Nuclear Network.

“Russia and North Korea’s public displays of their willingness to strengthen military ties, in particular, appear to suggest there is more to come soon, and it won’t necessarily all happen behind closed doors,” he said.

--With assistance from Sangmi Cha and James Herron.

(Updates with report of North Korean minister in Moscow in paragraph four.)