Russian President Vladimir Putin has accepted an invitation to visit North Korea, Pyongyang's state media said Thursday, as Kim Jong Un wrapped up a rare trip to meet with his ally.
The isolated Kim, who seldom leaves his country and has not travelled since before the pandemic, had a "historic meeting and talks" with Putin on Wednesday, the Korean Central News Agency said.
Among the results of the leaders' summit were Russian promises of help with North Korea's fledgling space programme, according to Russian news agencies, while Putin told reporters he saw "possibilities" for military cooperation.
Historic allies, Russia and the North are both under rafts of global sanctions -- Moscow for its Ukraine conflict, Pyongyang for its nuclear tests -- with Kim's visit sparking widespread concern over illicit arms agreements.
The head of South Korea's ruling party slammed what he called "a devil's deal" between Moscow and Pyongyang, with Japan warning Thursday against any violations of UN bans on arms deals with the North after Putin-Kim talks.
"We are watching (the talks) with concerns including the possibility that it could lead to violations of the Security Council's ban on all arms-related material transactions with North Korea," new Foreign Minister Yoko Kamikawa told reporters.
After touring a space centre and attending a lavish banquet in his honour, Kim "courteously invited Putin to visit the DPRK at a convenient time", state-run KCNA said, referring to the country by its official name.
"Putin accepted the invitation with pleasure and reaffirmed his will to invariably carry forward the history and tradition of the Russia-DPRK friendship."
Kim told Putin on Wednesday he was sure Russia would win a "great victory" over its enemies.
"We will always be with Russia," Kim said, according to footage broadcast on Russian TV.
"An old friend is better than two new ones," Putin said, quoting a Russian proverb and referencing the Soviet Union's role in the Korean War.
Kim then "said goodbye to Putin, wishing him good health" and headed to his next destination, KCNA said, with Putin earlier saying Kim would oversee a display of Russian warships in the far eastern city of Vladivostok to "demonstrate the capabilities of the Pacific Fleet".
Western countries have repeatedly raised concerns of a possible arms agreement between Russia and North Korea, as Moscow's war in Ukraine grinds on.
"The summit signals a seismic change in the Northeast Asian geopolitics," said Kim Jong-dae, a former MP and visiting scholar at Yonsei Institute for North Korean Studies.
A stronger alliance between North Korea, Russia and China could become a "destabilising force in the region", and ammunition from Pyongyang could significantly impact the war in Ukraine.
"I think Russia has already tested the North Korean shells in battlefields and is now ready to expand its use going forward. And neither the US nor South Korea has come to grips with the implications of such an arms deal between Russia and the North," he said.
Russia became a pariah in the West after invading Ukraine last year and has looked to strengthen alliances with other leaders facing similar isolation.
Putin on Wednesday praised the "strengthening of cooperation and friendship between our countries", while hosting Kim at a spaceport in Russia's far east.
He also said Moscow could help Pyongyang build satellites — after the North failed twice recently to put a military spy satellite into orbit.
In Washington, State Department spokesman Matthew Miller said any cooperation would be "quite troubling and would potentially be in violation of multiple UN Security Council resolutions".
Kim, who travelled overland to Russia in his bullet-proof train, was accompanied by a military-heavy entourage, with top Russian military officials including Defence Minister Sergei Shoigu also involved in the talks.
"With Kim Jong Un's latest visit to Russia, North Korea-Russia relations can be said to have completely returned to the level of blood alliance during the Cold War," Cheong Seong-chang, researcher at the Sejong Institute, told AFP.
"There have been many summit meetings between North Korea and Russia so far, but there has never been a time when North Korea brought in almost all of its key military officials like the one happening right now."