Russian President Vladimir Putin congratulated North Korean leader Kim Jong Un on Saturday on the 75 anniversary of the country's founding and called for stronger ties "on all fronts".

"I am convinced that thanks to our joint efforts we will continue to strengthen... bilateral ties on all fronts", Putin said in a message to Kim as quoted by the Kremlin.

"This fully corresponds to the interests of our people" and helps to ensure "the security and stability on the Korean peninsula and northeast Asia," he said.

Putin noted that the Soviet Union was the first country to recognise the North Korean regime and said that "since then relations between our two countries have always been based on the principles of friendship, good neighbourliness and mutual respect".

"I sincerely wish you good health and success and I wish all North Korean citizens peace and prosperity," Putin added.

The statement comes amid rumours of a possible summit between the two leaders in Russia later this month, according to US media reports.

American officials told the New York Times that Kim would likely travel by armoured train to Vladivostok, on Russia's Pacific coast not far from North Korea, to meet with Putin.

Vladivostok will be hosting the Eastern Economic Forum on September 10 to 13, which last year saw 68 countries attend.

The Kremlin however refused for the second time on Saturday to confirm any meeting.

"No, I don't know," said Kremlin spokesman Dmitry Peskov, when asked if he had information about a meeting between Putin and Kim on the sidelines of the summit.