Russian President Vladimir Putin signed Wednesday a mutual defence agreement with North Korea's Kim Jong Un, who offered his "full support" on Ukraine.

The pledge of military cooperation was part of a strategic treaty signed during a summit in Pyongyang, where Putin was making his visit in 24 years.

"It is really a breakthrough document," Putin said at a press conference in the North Korean capital, adding that it provided, "among other things, for mutual assistance in case of aggression against one of the parties to this treaty," Russian news agencies reported.

The two countries have been allies since North Korea's founding after World War II, and have drawn even closer after Russia's invasion of Ukraine in 2022 isolated Putin on the global stage.

The United States and its allies have accused North Korea of providing ammunition and missiles to Russia for its war in Ukraine, and the treaty was certain to fuel concerns of more deliveries.

Putin also said Russia "does not rule out military-technical cooperation with the DPRK in connection with the treaty that was signed today," referring to the North by its official name.

Kim called Putin the "dearest friend of the Korean people" and said his country "expresses full support and solidarity to the Russian government" over the war in Ukraine, which has triggered rafts of UN sanctions on Moscow.

Putin, in turn, thanked his host Kim -- himself under a decade-long UN sanctions regime over his banned weapons programs -- saying Moscow appreciated the "consistent and unwavering" support.

Putin said the two heavily sanctioned countries would not tolerate Western "blackmail", and that UN sanctions on North Korea should be reviewed.

"I am noting that the indefinite restrictive regime inspired by the US and its allies at the UN Security Council towards the DPRK should be reviewed," Putin said.

- Red carpet -

Putin arrived in Pyongyang before dawn on Wednesday to be greeted by Kim on a red carpet where the pair embraced and smiled.

They then attended a welcoming ceremony in Kim Il Sung square, featuring a military band and mass synchronised dancing, afer which Putin invited his host to visit Moscow.

The summit, which included a lengthy one-on-one chat between the leaders, was their second meeting in a year.

Kim took his bulletproof train to Russia's far east last September for a summit with Putin at a space port.

- Needs weapons -

The two Koreas have remained technically at war since their 1950-53 conflict and the border dividing them is one of the most heavily fortified in the world.

This week's visit was a way for Putin to thank the North "for acting as an 'arsenal for autocracy' in support of his illegal invasion of Ukraine," said Leif-Eric Easley, a professor at Ewha University in Seoul.

It was also part of Russia's drive to secure "strategic space" in Northeast Asia to counter US influence in the region, Seoul-based Institute for National Security Strategy's senior research fellow Kim Sung-bae told AFP.

"This intention is further evidenced by Putin's visit to Vietnam," he said, with the Russian leader set to fly to Hanoi after his trip to the North.