The streets of the North Korean capital were lined Wednesday with cheering crowds, mounted soldiers and grand portraits — not for Kim Jong Un, but for his guest and growing ally, Vladimir Putin.

The Russian president is meeting with the North Korean leader in a rare visit to the reclusive state, as he seeks ammunition for his war in Ukraine and vows to back the nuclear-armed regime against the United States.

U.S. officials previously told NBC News that they expect the pair to solidify a new deal to expand transfers of military technology to Pyongyang in exchange for supplies of munitions that Moscow's military badly needs on the battlefield.

Putin’s visit, his first to North Korea in 24 years, comes as the Kremlin’s forces push for breakthroughs in Ukraine’s east and north while Kyiv’s defenses have been bolstered by new commitments from its own allies.

Kim, meanwhile, has intensified his nuclear testing and threats, stoking tensions with U.S. ally South Korea and raising alarm about the extent of his ambitions.

Putin arrived at midday for a welcome ceremony at central Pyongyang’s Kim Il Sung Square, which is named after Kim’s grandfather and North Korea’s founder. Standing before a large crowd of cheering civilians, the two leaders greeted officials on a red carpet outside the city’s central library, from which two giant portraits of them stared down. Military bands played the two countries’ national anthems, and children waved balloons and the Russian and North Korean flags.

Kim and Putin then left for summit talks at the Kumsusan Palace.

“We highly appreciate your consistent and unwavering support for Russian policy, including on Ukraine,” Putin said in opening remarks before the start of the talks, according to Russian state media.

He also said Russia was fighting “the imperialist policy the United States and its satellites imposed for decades against Russia.”

Kim said Russia-North Korea relations were “entering a new period of high prosperity,” and pledged “full support” for Russia’s war in Ukraine, Russian state media reported.

Earlier, Kim was at Pyongyang International Airport to greet Putin upon his arrival in the early hours of Wednesday, shaking his hand and embracing him, according to the state-run Korean Central News Agency. He then accompanied Putin in his limousine to the Kumsusan State Guest House where the Russian leader would be staying.

The agency said the two leaders “exchanged their pent-up inmost thoughts” during the ride and that their meeting demonstrated the “invincibility and durability” of Russia-North Korea ties.

Putin last visited Pyongyang in 2000 to improve ties with Kim’s father, Kim Jong Il, while the current North Korean leader’s visit to Russia’s far east last year offered signs of the deepening relationship.

In a letter published in North Korean state media on Tuesday ahead of the trip, Putin said he appreciated the country’s support for the war in Ukraine and vowed to support Pyongyang against U.S. “economic pressure, provocation, blackmail and military threats.”

The highlight of the visit is expected to be a new strategic agreement that could deepen military and economic cooperation between the two regimes as they look to bypass the slew of global sanctions against them. On Wednesday, Putin called it a “fundamental document” that will “create the basis of our relations long term.”

The leaders’ itinerary also includes individual speeches, a tea party and a “ceremonial concert” to be held at a sports complex, Putin’s foreign policy aide Yuri Ushakov said Monday, according to Russian state media.

The strategic agreement could “lay the groundwork for arms trade and also facilitate their anti-U.S. and anti-West coalition,” said Lami Kim, a professor at the Daniel K. Inouye Asia-Pacific Center for Security Studies in Honolulu.

Officials in the West are concerned about weapons and intelligence sharing that could both help Putin’s army in Ukraine, and threaten the U.S. and its allies in Asia.

Secretary of State Antony Blinken said Tuesday that Russia was trying “in desperation, to develop and to strengthen relations with countries that can provide it with what it needs to continue the war of aggression that it started against Ukraine.”

He said North Korea had been providing Russia with “significant munitions” as well as other weapons for use in Ukraine.

U.S. intelligence officials believe Putin is providing North Korea with nuclear submarine and ballistic missile technology in exchange, six senior U.S. officials have told NBC News. The Biden administration, they said, is concerned that Russia might help North Korea complete the final steps needed to field its first submarine capable of launching a nuclear-armed missile.

Both North Korea and Russia have denied any transfer of arms, which would be in violation of United Nations Security Council resolutions that Russia has supported in the past.

Russia ended the monitoring of U.N. sanctions against North Korea with a veto in the Security Council earlier this year that drew accusations that Moscow was avoiding scrutiny and joining China in shielding Kim from consequences for his weapons tests.

The South Korean Foreign Ministry said Tuesday that any cooperation must not violate the existing resolutions and “undermine regional peace and stability.”

Pyongyang may also get access to much-needed oil and natural resources for its decimated economy and missile program.

“Their cooperation will further undermine the effectiveness of sanctions,” Kim, the professor in Honolulu, said.

It’s also a personal win for the North Korean leader, she said, as “being seen with a world leader like Putin would also be a huge win” for domestic propaganda efforts to elevate him to the cult-like status that his father and grandfather enjoyed.

“There’s economic gains and reputational gains,” she said.

Tensions on the Korean Peninsula are at their highest point in years, as Kim accelerates weapons testing and the U.S., South Korea and Japan intensify joint military drills that the North views as a rehearsal for invasion. Last year Kim cast aside the goal of unifying with the South, raising concerns that he may be preparing for an all-out attack on the U.S. ally.

The rival neighbors have stepped up psychological warfare, exchanging waste-filled balloons and music on loudspeakers. South Korean troops fired warning shots Tuesday after North Korean soldiers briefly crossed the heavily fortified border, apparently in error.

The two remain technically at war after the Korean War ended in 1953 with an armistice rather than a peace treaty.

After leaving North Korea on Wednesday, Putin is expected to visit Vietnam, which upgraded its relationship with the U.S. during a visit by President Joe Biden last year.

The U.S. rebuked Vietnam over the visit, with a State Department spokesperson telling NBC News: “No country should give Putin a platform to promote his war of aggression and otherwise allow him to normalize his atrocities.”