Kim's trip is still unconfirmed. It was first reported by the New York Times citing unidentified U.S. officials and South Korea's intelligence agency said it was possible. But state media in both North Korea and Russia have been silent.

The Kremlin said it had "nothing to say" on the matter, though President Vladimir Putin is due to speak this week at an economic forum in Russia's Pacific port of Vladivostok, 6,500 km (4,000 miles) east of Moscow.

One source who spoke on condition of anonymity told Reuters that a Kim visit was expected in coming days. Russia's Interfax news agency citied several unidentified sources as saying that Kim was due to visit Russia's far east shortly.

Kim appears to have departed for Russia on a train, South Korean broadcaster YTN reported on Monday, citing a government source.

Vladivostok is just 130 km (80 miles) from Russia's border with North Korea. If he does make the trip, it would be only his second known visit to Russia.

In Vladivostok, there was a higher police presence than usual on the streets but no North Korean flags had been put up - unlike last time when the city was adorned with the red five pointed stars that grace the Communist country's flag.

In Vladivostok's central square beside a monument to Red Army soldiers, Russians said they were awaiting Kim's visit.

"Both countries show teeth to the whole world and can stand for themselves. So, there is something in common," said Vladivostok resident Fyodor, who refused to give his surname.

Others pointed to the economic forum which Putin was attending.

"A forum is taking place, so it all adds up - he'll come," said Nikolai, who also declined to give his surname. "The security will be running after his limousine again."

NORTH KOREA

During the Cold War, Moscow supported North Korea though relations were complicated when China's Mao Zedong split with the Kremlin over its aim for peaceful coexistence with the West.

After the 1991 collapse of the Soviet Union, relations cooled amid the chaos in Russia and China is considered the most powerful influence on Pyongyang.

The United States has expressed concern over what it calls advancing arms negotiations between the two countries, with White House National Security Adviser Jake Sullivan urging Kim "not to supply weapons to Russia that will end up killing Ukrainians".

Analysts say North Korea has huge supplies of artillery shells, rockets and small arms ammunition that could help Russia replenish the vast stocks it has expended in more than 18 months of war in Ukraine.

In return, Russia could offer grain, oil and military technology as Kim looks to develop capabilities such as nuclear-powered submarines and military reconnaissance satellites.

"Maybe they will be friends with us, but not likely with the U.S.," said Yelena, a tourist from Khabarovsk, a Russian city on the Amur River bordering China.

The United States has accused North Korea of providing arms to Russia, but it is unclear whether any deliveries have been made. Both Russia and North Korea have denied those claims, but promised to deepen defence cooperation.

The most striking sign of that came in July, when Russian Defence Minister Sergei Shoigu visited Pyongyang and toured a weapons exhibit that included the North's banned ballistic missiles. He later stood beside Kim and saluted the missiles as they rolled by during a military parade.

"He (Kim Jong Un) is such a cryptic person, so I don't even know if he will come or not," said Vladivostok resident Svetlana. "But I think he must come - we have some changes going on, so it must be interesting for him what happens in Russia."

(Reporting by Reuters in Vladivostok; Writing by Guy Faulconbridge and Mark Trevelyan; Editing by Nick Macfie)