SEOUL, South Korea — Russian President Vladimir Putin arrived in North Korea on Tuesday in a rare visit to the reclusive Communist state as he seeks support from leader Kim Jong Un in his war against Ukraine.

Putin’s two-day visit, his first to North Korea in 24 years, comes as North Korean soldiers briefly crossed the heavily fortified border between North and South Korea for the second time this month, drawing warning shots from South Korean soldiers.

In a letter published Tuesday in Rodong Sinmun, the mouthpiece of North Korea’s ruling Workers’ Party, Putin expressed appreciation for North Korea’s support in what he calls Russia’s “special military operation” in Ukraine.

He said he would in turn support North Korea’s efforts to defend its interests in the face of what he called decades of “U.S. economic pressure, provocation, blackmail and military threats.”

Putin also alluded to what appears to be the two countries’ growing alignment in their animosity toward the West, which is concerned about the transfer of arms and intelligence that could fuel Putin’s ambitions in Ukraine and Kim’s dreams of becoming an internationally recognized nuclear state.

Russian state media reported Tuesday that the two countries would sign a comprehensive strategic partnership agreement during Putin’s visit. Putin foreign policy aide Yuri Ushakov said earlier that the agreement “will not be directed against any countries but is aimed at ensuring greater stability in the Northeast Asia region.”

North Korea has long been under U.N. Security Council sanctions over its nuclear weapons and missile programs, while Russia is also increasingly isolated by Western sanctions over its war in Ukraine. North Korea is seen as a critical source of military support to replenish Russia’s draining arsenal.

State Department spokesperson Matthew Miller said Monday that Putin had become “incredibly desperate over the past few months” amid setbacks in Ukraine and was seeking help from North Korea and Iran. He said North Korea had unlawfully transferred dozens of ballistic missiles and more than 11,000 containers of munitions to Russia in recent months.

Both countries have denied any transfer of arms, which would be in violation of U.N. Security Council resolutions.

A spokesperson for the South Korean Foreign Ministry said ahead of the visit that cooperation between Russia and North Korea must not violate U.N. Security Council resolutions and that it had conveyed that message to Russia.

Ukrainian Foreign Minister Dmytro Kuleba on Monday dismissed what he called Kim and Putin’s “lonely bromance.” He told Agence France-Presse that the best way to respond was to “continue strengthening the diplomatic coalition for just and lasting peace in Ukraine” and deliver more Western air defense systems and weapons.

Though they are likely to continue issuing denials, North Korea and Russia have “notably shifted from hiding their illicit activities to flaunting their cooperation,” said Leif-Eric Easley, a professor of international studies at Ewha Womans University in Seoul. 

“Putin’s visit is in part to thank North Korea for acting as an ‘arsenal for autocracy’ in support of his illegal invasion of Ukraine,” he said in an email.

The visit also allows North Korean state media to portray Kim as a world leader, Easley added. It follows a visit by Kim last September to Russia’s Far East, where he toured a Russian spaceport and Putin suggested that Russia could help North Korea develop satellites.

Last week, Kim boasted about the ties between the two countries, saying that North Korea was an “invincible comrade-in-arms” with Russia in a message to Putin marking Russia’s National Day.

Ushakov said Monday that Putin’s North Korea visit would include one-on-one talks, a state reception, an honor guard and a statement to the media. Other members of the delegation include Foreign Minister Sergei Lavrov, Defense Minister Andrei Belousov and the head of the Russian space agency.

Hours before Putin’s arrival, South Korean officials said as many as 30 North Korean soldiers had illegally crossed the military demarcation line within the Demilitarized Zone, which separates North and South Korea. The two countries are technically still at war after the 1950-53 Korean War ended with an armistice rather than a peace treaty.

The North Korean soldiers, some of whom were heavily armed, retreated to the North Korean side when the South Korean military broadcast warning messages and fired warning shots, South Korea’s Joint Chiefs of Staff said.

The border crossing occurred at a different location than a similar brief intrusion on June 9 that South Korean authorities believe was also not deliberate.

On both occasions, the North Korean soldiers were conducting a range of work along the border including planting mines, erecting walls and building roads for military operations, South Korean officials said. Such work has been underway since November, when North Korea said it was suspending a 2018 military agreement aimed at reducing tensions between the two Koreas.

South Korea said this month that it was also fully suspending the agreement in response to a series of trash-filled balloons that the North sent toward the South.

South Korean officials said Tuesday that they believe there have been multiple casualties among North Korean soldiers due to the explosion of North Korean land mines along the border.

“North Korean soldiers are unreasonably continuing with their labor despite these accidents and casualties,” they said.

Stella Kim reported from Seoul, South Korea, and Mithil Aggarwal reported from Hong Kong.