The Kremlin said on Tuesday it was unable to confirm a summit between Putin and Kim. "We have nothing to say on this," Kremlin spokesman Dmitry Peskov said.
The White House's National Security Council (NSC) spokeswoman Adrienne Watson said "arms negotiations between Russia and the DPRK are actively advancing," using an acronym for North Korea.
"We have information that Kim Jong Un expects these discussions to continue, to include leader-level diplomatic engagement in Russia," she added.
The United States warned last week that Russia was already in secret talks with the North to acquire a range of munitions and supplies for Moscow's war effort.
Kim is likely to head by armored train later this month to Vladivostok, on Russia's Pacific coast not far from North Korea, to meet Putin, US and other officials told the New York Times.
Vladivostok is hosting the Eastern Economic Forum from September 10–13, which was attended by representatives from 68 countries last year.
According to the Times, Putin is seeking artillery shells and antitank missiles from North Korea, while Kim, who could even travel to Moscow, is reportedly in search of advanced technology for satellites and nuclear-powered submarines, as well as food aid for his impoverished nation.
An official at Seoul's unification ministry, which handles inter-Korean relations, said various developments "indicated" the growing possibility of an arms deal between Pyongyang and Moscow.
"Any form of cooperation between North Korea and neighboring countries must be conducted in a way that does not undermine international norms and peace," he told reporters.
Washington said last week that, despite its denials, North Korea supplied infantry rockets and missiles to Russia in 2022 for use by the privately controlled Wagner military group.
Russian Defense Minister Sergei Shoigu traveled to North Korea in July seeking to acquire additional munitions for the war, Watson said Monday.
- Diplomatic isolation -
Park Won-gon, a professor at Ewha University in Seoul, said both Pyongyang and Moscow needed to "break away from diplomatic isolation," and a summit would send a message to Washington, which is ramping up defence cooperation with South Korea and Japan.
"As South Korea, the United States, and Japan have recently been strengthening cooperation, including the Camp David summit, North Korea and Russia also need to showcase their cooperation in a symbolic diplomatic sense," he told AFP.
Last week at the United Nations, the United States, Britain, South Korea and Japan said that any deal to increase cooperation between Russia and North Korea would violate Security Council resolutions forbidding arms deals with Pyongyang -- resolutions Moscow itself had endorsed.
They said another group of Russian officials traveled to North Korea for follow-up talks after Shoigu's visit to Pyongyang.
Cho Han-bum, a senior research fellow at the Korea Institute for National Unification, said sanctions will do little to stop Russia and North Korea from trading weapons.
"The war in Ukraine and the strategic competition between the United States and China have virtually neutralised the current UN Security Council system," Cho told AFP.
Moscow and Pyongyang had "no worries" about sanctions because both countries were already operating under an array of Western punitive measures, he said, adding that military cooperation between the two was likely "unstoppable".
The United States last month sanctioned three entities accused of seeking to facilitate arms deals between North Korea and Russia as Washington tightened restrictions on support for Moscow's war in Ukraine.
The US Treasury Department said Russia was continuing to use up munitions and lose heavy equipment in Ukraine, forcing it to turn to its small pool of allies, including North Korea, for support.
Ukrainian officials have claimed some progress in their counteroffensive, but Putin said again on Monday the attempt to retake land lost since Russia's February 2022 invasion had been unsuccessful.
"It is not that it is stalling. It is a failure," Putin said during a news conference with Turkish leader Recep Tayyip Erdogan in the Black Sea resort city of Sochi.
"At least today this is what it looks like. Let's see what happens next."
News of the likely meeting between Kim and Putin came as Ukrainian President Volodymyr Zelensky said he had visited his war-torn country's frontline eastern Donetsk region, posting a video of himself meeting soldiers.
