North Korea's Kim Jong Un rolled into Russia on an armored train Tuesday to see President Vladimir Putin, a rare meeting between isolated leaders driven together by their need for support in escalating standoffs with the West.

Kim is expected to seek economic aid and military technology for his impoverished country, and, in an unusual twist, appears to have something Putin desperately needs: munitions for Russia's grueling war in Ukraine.

This meeting is a chance for the North Korean leader to get around crippling U.N. sanctions and years of diplomatic isolation. For Putin, it's an opportunity to refill ammunition stores that the war has drained.

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Any arms deal with North Korea would violate the sanctions, which Russia supported in the past.

North Korea's official Korean Central News Agency said Kim boarded his personal train bound for Russia on Sunday afternoon, accompanied by members of the ruling party, government and military.

His final destination is uncertain. Many had assumed Kim and Putin would meet in Vladisvostok, a Russian city close to the border where the two leaders had their last meeting in 2019, and which Putin is visiting this week for an economic forum.

But Kremlin spokesman Dmitry Peskov confirmed only that Kim has entered Russia, and state news agency RIA-Novosti later reported his train had headed north after crossing the Razdolnaya River, taking it away from Vladivostok. The South Korean news agency Yonhap later published a photo that it said showed the train in Ussuriysk, a city about 60 kilometers north of Vladivostok that has a sizeable ethnic Korean population.

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Some Russian news media speculate that he is headed for the Vostochny spaceport, which Putin is to visit soon. Putin declined during the forum to say what he intended to do there. The launching facility is about 900 kilometers (550 miles) northwest of Ussuriysk, but the route there is circuitous and it is unclear how long Kim's slow-moving train would take to get there.

Peskov said Putin and Kim will meet after the Vladivostok forum, and that the meeting would include a lunch in Kim's honor.

Officials identified in North Korean state media photos may hint at what Kim might seek from Putin and what he would be willing to give.

Kim is apparently accompanied by Jo Chun Ryong, a ruling party official in charge of munitions policies who joined the leader on recent tours of factories producing artillery shells and missiles, said South Korea's Unification Ministry. Russian Defense Minister Sergei Shoigu will be part of the Russian delegation, according to Peskov.

North Korea may have tens of millions of aging artillery shells and rockets based on Soviet designs that could give a huge boost to the Russian army in Ukraine, analysts say.

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Also identified in photos were Pak Thae Song, chairman of North Korea's space science and technology committee, and Navy Adm. Kim Myong Sik, who are linked with North Korean efforts to acquire spy satellites and nuclear-capable ballistic missile submarines. Experts say North Korea would struggle to acquire such capabilities without external help, although it's not clear if Russia would share such sensitive technologies.

Kim Jong Un may also seek badly needed energy and food supplies, analysts say. Deputy foreign minister Andrei Rudenko said Russia may discuss humanitarian aid with the North Korean delegation, according to Russian news agencies.

Kim's delegation also likely includes his foreign minister, Choe Sun Hui, and his top two military officials, Korean People's Army Marshals Ri Pyong Chol and Pak Jong Chon.

Data from FlightRadar24.com, which tracks flights worldwide, showed an Air Koryo Antonov An-148 took off from Pyongyang on Tuesday and flew for about an hour to reach Vladivostok. North Korea's national airline has only just resumed flying internationally after being grounded during the COVID-19 pandemic. There had been speculation that North Korea could use a plane to fly in support staff.

Kim is making his first foreign trip since the pandemic, during which North Korea imposed tight border controls for more than three years. After decades of hot-and-cold relations, Russia and North Korea have drawn closer since Moscow's invasion of Ukraine in 2022.

Lim Soo-suk, South Korea's Foreign Ministry spokesperson, said Seoul was maintaining communication with Moscow while closely monitoring Kim's visit.

"No U.N. member state should violate Security Council sanctions against North Korea by engaging in an illegal trade of arms, and must certainly not engage in military cooperation with North Korea that undermines the peace and stability of the international community," Lim said during a briefing.

U.S. officials released intelligence last week that North Korea and Russia were arranging a meeting between their leaders.

According to U.S. officials, Putin could focus on securing more supplies of North Korean artillery and other ammunition to refill declining reserves as he seeks to rebuff a Ukrainian counteroffensive and show that he's capable of grinding out a long war of attrition. That could potentially put more pressure on the U.S. and its partners to pursue negotiations as concerns over a protracted conflict grow despite their huge shipments of advanced weaponry to Ukraine in the past 17 months.

"Arms discussions between Russia and the DPRK are expected to continue during Kim Jong Un's trip to Russia," said White House National Security Council spokesperson Adrienne Watson, using the abbreviation for North Korea's official name of the Democratic People's Republic of Korea. "We urge the DPRK to abide by the public commitments that Pyongyang has made to not provide or sell arms to Russia."

State Department spokesman Matthew Miller said Washington will monitor the meeting closely, reminding both countries that "any transfer of arms from North Korea to Russia would be a violation of multiple U.N. Security Council resolutions," and that the U.S. "will not hesitate to impose new sanctions."

Japan's Chief Cabinet Secretary Hirokazu Matsuno told reporters that Tokyo will be watching the outcome of the Kim-Putin meeting with concern, including the "impact it could have on Russia's invasion of Ukraine."

The United States has accused North Korea of providing Russia with arms, including selling artillery shells to the Russian mercenary group Wagner. Both Russian and North Korean officials denied such claims.

But speculation about the countries' military cooperation grew after Shoigu, the defense minister, made a rare visit to North Korea in July, when Kim invited him to an arms exhibition and a massive military parade in the capital where he showcased ICBMs designed to target the U.S. mainland.

Following that visit, Kim toured North Korea's weapons factories, including a facility producing artillery systems where he urged workers to speed up the development and large-scale production of new kinds of ammunition. Experts say Kim's visits to the factories likely had a dual goal of encouraging the modernization of North Korean weaponry and examining artillery and other supplies that could be exported to Russia.