SEOUL — A North Korean train presumably carrying leader Kim Jong Un is on the way to Russia for a possible meeting with President Putin, South Korean press said Monday.

Citing unidentified South Korean government sources, the Chosun Ilbo newspaper reported that the train likely left the North Korean capital of Pyongyang on Sunday evening and that a Kim-Putin meeting is possible as early as Tuesday.

The Yonhap news agency and some other media published similar reports. Japan’s Kyodo news agency cited Russian officials as saying that Kim was possibly heading for Russia in his personal train.

South Korea’s Presidential Office, Defense Ministry and National Intelligence Service didn’t immediately confirm those details.

American officials released intelligence last week that North Korea and Russia were arranging a meeting between their leaders that would take place within this month as they expand their cooperation in the face of deepening confrontations with the United States. 

A possible venue for the meeting is the eastern Russian city of Vladivostok, where Mr. Putin arrived Monday to attend an international forum that runs through Wednesday, according to Russia’s TASS news agency. The city was also the site of Mr. Putin’s first meeting with Mr. Kim in 2019.

According to American officials, Mr. Putin could focus on securing more supplies of North Korean artillery and other ammunition to refill declining reserves as he seeks to defuse 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 United States and its partners to pursue negotiations as concerns about a protracted conflict grow despite their huge shipments of advanced weaponry to Ukraine over the past 17 months.

North Korea has possibly tens of millions of artillery shells and rockets based on Soviet designs that could potentially give a huge boost to the Russian army, analysts say.

In exchange, Mr. Kim could seek badly needed energy and food aid and advanced weapons technologies, including those related to intercontinental ballistic missiles, nuclear-capable ballistic missile submarines and military reconnaissance satellites, analysts say.

There are concerns that potential Russian technology transfers would increase the threat posed by Mr. Kim’s growing arsenal of nuclear weapons and missiles that are designed to target the United States, South Korea, and Japan.

After a complicated, hot-and-cold relationship for decades, Russia and North Korea have been drawing closer to each other since Russia’s invasion of Ukraine in February 2022. 

The bond has been driven by Mr. Putin’s need for war help and Mr. Kim’s efforts to boost the visibility of his partnerships with traditional allies Moscow and Beijing as he tries to break out of diplomatic isolation and have North Korea be part of a united front against Washington.

While using the distraction caused by the Ukraine conflict to ramp up its weapons development, North Korea has repeatedly blamed the United States for the crisis in Ukraine, claiming the West’s “hegemonic policy” justified a Russian offensive in Ukraine to protect itself.

North Korea is the only nation other than Russia and Syria to recognize the independence of two Russian-backed separatist regions in eastern Ukraine — Donetsk and Luhansk — and it has also hinted at an interest in sending construction workers to those areas to help with rebuilding efforts.

Russia — along with China — has blocked American-led efforts at the UN Security Council to strengthen sanctions on North Korea over its intensifying missile tests while accusing Washington of worsening tensions with Pyongyang by expanding military exercises with South Korea and Japan.

The United States has been accusing North Korea since last year of providing Russia with arms, including artillery shells sold to the Russian mercenary group Wagner. Both Russian and North Korean officials denied such claims. 

Yet speculation about the countries’ military cooperation grew after Russia’s defense minister, Sergei Shoigu, made a rare visit to North Korea in July, when Mr. 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 Mr. Shoigu’s visit, Mr. 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 Mr. 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 possibly be exported to Russia.

President Biden’s chief deputy national security adviser, Jon Finer, told reporters on Sunday that buying weapons from North Korea “may be the best and may be the only option” open to Moscow as it tries to keep its war effort going.

“We have serious concerns about the prospect of North Korea potentially selling weapons, additional weapons, to the Russian military. It is interesting to reflect for a minute on what it says that when Russia goes around the world looking for partners that can help it, it lands on North Korea,” Mr. Finer said aboard a plane carrying Biden to Vietnam from India.

Some analysts say a potential meeting between Messrs. Kim and Putin would be more about symbolic gains than substantial military cooperation.

Russia — which has always closely guarded its most important weapons technologies, even from key allies such as China — could be unwilling to make major technology transfers with North Korea for what is likely to be limited war supplies transported over a small rail link between the countries, they say.