Russian President Vladimir Putin yesterday signed a deal with North Korea's Kim Jong Un that included a mutual defence pledge, one of Russia's most significant moves in Asia for years that Kim said amounted to an "alliance".

Putin's pledge overhauls Russia's entire post-Soviet policy on North Korea just as the United States and its Asian allies try to gauge how far Russia could deepen support for the only country to have tested a nuclear weapon this century.

On his first visit to Pyongyang since July 2000, Putin explicitly linked Russia's deepening of ties with North Korea to the West's growing support for Ukraine and said Moscow could develop military and technical cooperation with Pyongyang.

After talks, they signed a "comprehensive strategic partnership" pact, which Putin said included a mutual defence clause in the case of aggression against either country.

"The comprehensive partnership agreement signed today provides, among other things, for mutual assistance in the event of aggression against one of the parties to this agreement," Putin said.

He said Western deliveries of advanced, long-range weaponry including F-16 fighters to Ukraine for strikes against Russia breached major agreements.

"In connection with this, Russia does not exclude for itself the development of military-technical cooperation with the Democratic People's Republic of Korea," Putin said.

Kim praised Russia for making what he cast as an enormously significant strategic move to support North Korea, which was founded in 1948 with the Soviet Union's backing.

Putin's courting of Kim, which has included gifts of limousines and a tour of Russia's new space launch centre, has alarmed the United States and its Asian allies.

Putin was greeted by cheering crowds lining the streets of Pyongyang along with children waving Russian flags and a military salute. Kim, 40, greeted Putin at the airport.

After talks, Putin drove Kim around in a luxury Russian limousine. They then switched places and Kim drove Putin. Later, they watched a concert together.

Putin accused the United States, South Korea and Japan of raising tensions on the Korean peninsula and said North Korea had a right to strengthen its own defences.

Kim said the pact would expand cooperation in politics, economy and defence, calling it "strictly peace-loving and defensive" in nature.

"Our two countries' relations have been elevated to the new higher level of an alliance," Kim said.

At the start of their summit, Kim expressed "unconditional support" for "all of Russia's policies", including "a full support and firm alliance" for Putin's war with Ukraine.

Putin said Moscow was fighting the hegemonic, imperialist policy of the United States and its allies, Russian media reported.

"We highly appreciate your consistent and unwavering support for Russian policy, including in the Ukrainian direction," Putin said.

The countries' partnership was an "engine for accelerating the building of a new multi-polar world", North Korea's state news agency KCNA said.

Russia has used its warming ties with North Korea to needle Washington, while heavily sanctioned North Korea has won political backing and promises of economic support and trade from Moscow.

The United States and its allies say they fear Russia could provide aid for North Korea's missile and nuclear programmes, which are banned by UN Security Council resolutions, and have accused Pyongyang of providing ballistic missiles and artillery shells that Russia has used in its war in Ukraine.