SEOUL — North Korea’s leader, Kim Jong-un, vowed support for Russia’s “just fight” during a summit with President Putin on Wednesday that America warned could lead to a deal to supply ammunition for Moscow’s war in Ukraine.

After touring launch pads with Mr. Putin at a remote space base in Russia’s Far East, Mr. Kim expressed “full and unconditional support” and said Pyongyang will always stand with Moscow on the “anti-imperialist” front.

The leaders met at the Vostochny Cosmodrome for a summit that underscores how their interests are aligning in the face of their countries’ separate, intensifying confrontations with the United States. 

The talks lasted four to five hours, after which Mr. Kim left, Russia’s state news agency RIA Novosti reported.

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.

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 have denied such claims.

That would be a striking reversal of roles: the Soviet Union provided ammunition, warplanes and pilots to support communist North Korea’s invasion of the South during the 1950-53 Korean War, and the North relied on Soviet economic aid for decades afterward.

The decision to meet at the cosmodrome, Russia’s most important launch center on its own soil, suggests that in return Mr. Kim is seeking Russian help to develop military reconnaissance satellites, which he has described as crucial to enhance the threat of his nuclear-capable missiles. 

In recent months, North Korea has repeatedly failed in attempts to put its first military spy satellite into orbit.

But either buying arms from or providing rocket technology to North Korea would violate international sanctions that Russia has supported in the past.

Mr. Putin met Mr. Kim’s limousine, brought from Pyongyang in the North Korean leader’s special armored train, at the entrance to the launch facility, greeting his guest with a handshake that lasted around 40 seconds. 

In his opening remarks, Mr. Putin talked about the Soviet Union’s wartime support for North Korea and said the talks would cover economic cooperation, humanitarian issues and the “situation in the region.”

Mr. Kim, in turn, expressed support for Moscow, making an apparent reference to the war in Ukraine. “Russia is currently engaged in a just fight against hegemonic forces to defend its sovereign rights, security and interests,” the North Korean leader said. “I take this opportunity to affirm that we will always stand with Russia on the anti-imperialist front and the front of independence.”

The meeting came hours after North Korea fired two ballistic missiles toward the sea, extending a highly provocative run in North Korean weapons testing since the start of 2022, as Mr. Kim used the distraction caused by Mr. Putin’s war on Ukraine to accelerate his weapons development.