North Korean leader Kim Jong-un will soon visit Russia to meet President Vladimir Putin, the two countries confirmed on Monday, a potentially landmark summit amid Moscow's deepening isolation over the war in Ukraine.

Kim will visit Russia in the coming days at the invitation of Putin, the Kremlin said, while North Korean state news agency KCNA said the two would "meet and have a talk", without elaborating.

US officials have said the pair would discuss possible arms deals to aid Russia's war in Ukraine and provide North Korea with a much-needed economic and political lifeline.

Washington and its allies have been voicing concern at recent signs of closer military cooperation between Russia and the nuclear-armed North.

It will be Kim's second summit with Putin, after the pair met in 2019.

Despite denials by both Pyongyang and Moscow, the United States has said talks are advancing actively for North Korea to supply arms to Russia which has expended vast stocks of weapons in more than 18 months of war in Ukraine.

The North Korean leader appeared to have left aboard a special train bound for Russia, South Korean media reported on Monday, citing unnamed senior government sources, but neither Moscow nor Pyongyang immediately confirmed an exact schedule for the visit. (Reuters)