SEOUL--North Korean leader Kim Jong Un promised full support for Russia’s war in Ukraine before beginning a one-on-one meeting with Russian President Vladimir Putin in Pyongyang on Wednesday, in a bid to expand their economic and military cooperation and show a united front against Washington.

Speaking before the summit, Putin thanked Kim for support in Ukraine and said the two countries would sign an agreement to boost their partnership as both “fight against the imperialist hegemonistic policies of the U.S. and its satellites against the Russian Federation,” according to remarks carried by Russian state Tass and RIA Novosti news agencies.

Putin’s visit comes amid growing concerns about an arms arrangement in which North Korea provides Russia with badly needed munitions to fuel Moscow’s war in Ukraine, in exchange for economic assistance and technology transfers that could enhance the threat posed by Kim’s nuclear weapons and missile program.

North Korea is under heavy U.N. Security Council sanctions over its weapons program, while Russia also faces sanctions by the United States and its Western partners over its aggression in Ukraine.

After one-on-one talks, the two might issue a joint statement and Kim will host a reception, according to Russian media. Putin is expected to leave Wednesday evening for Vietnam.

Putin hailed ties that date to the Soviet army fighting the Japanese military on the Korean Peninsula in the closing moments of World War II, and Moscow’s support for Pyongyang during the Korean War.

Kim said relations between Moscow and Pyongyang are now even closer than during Soviet times and called Putin’s visit an opportunity to solidify their “fiery friendship.”

Kim vowed his country’s “full support and solidarity to the Russian government, army and people in carrying out the special military operation in Ukraine to protect sovereignty, security interests and territorial integrity.” It wasn’t immediately clear what that support might look like.

Kim has used similar language in the past, consistently saying North Korea supports what he describes as a just action to protect Russia’s interests and blaming the crisis on the U.S.-led West’s “hegemonic policy.”

He also hailed Russia’s “important role and mission in preserving the strategic stability and balance in the world.”

Before the talks, Kim welcomed Putin with a lavish ceremony in the city’s main square, where he introduced key members of the North Korean leadership including Foreign Minister Choe Son Hui; top aide and ruling party secretary Jo Yong Won; and the leader’s powerful sister, Kim Yo Jong.

Huge crowds lined up on the streets to greet Putin’s motorcade, chanting “Welcome Putin” and waving flowers and North Korean and Russian flags.

Putin was accompanied by several top officials, including Deputy Prime Minister Denis Mantrurov, Defense Minister Andrei Belousov and Foreign Minister Sergey Lavrov, according to his foreign policy adviser, Yuri Ushakov.

U.S. and South Korean officials accuse the North of providing Russia with artillery, missiles and other military equipment for use in Ukraine, possibly in return for key military technologies and aid. Both Pyongyang and Moscow deny accusations about North Korean weapons transfers, which would violate multiple U.N. Security Council sanctions that Russia previously endorsed.

Along with China, Russia has provided political cover for Kim’s continuing efforts to advance his nuclear arsenal, repeatedly blocking U.S.-led efforts to impose fresh U.N. sanctions on the North over its weapons tests.

In March, a Russian veto at the United Nations ended monitoring of U.N. sanctions against North Korea over its nuclear program, prompting Western accusations that Moscow is seeking to avoid scrutiny as it buys weapons from Pyongyang for use in Ukraine. U.S. and South Korean officials have said they are discussing options for a new mechanism for monitoring the North.

South Korean analysts say that Kim will likely seek stronger economic benefits and more advanced military technologies from Russia, although his more sensitive discussions with Putin aren’t likely to be made public.

While Kim’s military nuclear program now includes developmental intercontinental ballistic missiles that can potentially reach the U.S. mainland, he may need outside technology help to meaningfully advance his program further. There are already possible signs that Russia is assisting North Korea with technologies related to space rockets and military reconnaissance satellites, which Kim has described as crucial for monitoring South Korea and enhancing the threat of his nuclear-capable missiles.

The North may also seek to increase labor exports to Russia and other illicit activities to gain foreign currency in defiance of U.N. Security Council sanctions, according to a recent report by the Institute for National Security Strategy, a think tank run by South Korea’s main spy agency. There will likely be talks about expanding cooperation in agriculture, fisheries and mining and further promoting Russian tourism to North Korea, the institute said.

In Washington, U.S. Secretary of State Antony Blinken said Putin’s visit to North Korea illustrates how Russia tries, “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.”

“North Korea is providing significant munitions to Russia ... and other weapons for use in Ukraine. Iran has been providing weaponry, including drones, that have been used against civilians and civilian infrastructure,” Blinken told reporters following a meeting with NATO chief Jens Stoltenberg on Tuesday.

Tensions on the Korean Peninsula are at their highest point in years, with the pace of both Kim’s weapons tests and combined military exercises involving the United States, South Korea and Japan intensifying in a tit-for-tat cycle. The Koreas also have engaged in Cold War-style psychological warfare that involved North Korea dropping tons of trash on the South with balloons, and the South broadcasting anti-North Korean propaganda with its loudspeakers.