Russian President Vladimir Putin and North Korean leader Kim Jong Un have signed a comprehensive strategic partnership that includes a vow of mutual aid if either country is attacked.

Mr Putin and Mr Kim spoke face-to-face for about two hours during a summit in Pyongyang – a meeting that was originally planned for one hour, Russian state media said.

It was not clear what kind of assistance the partnership deal would call for, but it could mark the strongest connection between Moscow and Pyongyang since the end of the Cold War.

Both leaders described it as a major upgrade of their relations, covering security, trade, investment and cultural and humanitarian ties.

The Russian leader’s first visit to North Korea in 24 years comes amid growing concerns over an arms arrangement in which North Korea provides Russia with badly needed munitions for Moscow’s war in Ukraine, in exchange for economic assistance and technology transfers that could enhance the threat posed by Mr Kim’s nuclear weapons and missile programme.

Mr Putin and Mr Kim attend a gala concert in Pyongyang,
Details of what the pact entails are unclear at the moment (Sputnik, Kremlin Pool Photo via AP)

Speaking before the summit, Mr Putin thanked Kim for North Korea’s support in Ukraine and said the two countries would sign the agreement to boost their partnership as both “fight against the imperialist hegemonistic policies of the US and its satellites against the Russian Federation”.

North Korea is under heavy UN Security Council sanctions over its weapons programme, while Russia also faces sanctions by the US and its Western partners over its aggression in Ukraine.

Earlier on Thursday, Mr Putin travelled on to Vietnam for the next leg of his trip, where he will make a state visit to strengthen ties with a long-time partner.

Mr Kim and Mr Putin march on a red carpet
The leaders have vowed even closer cooperation (Sputnik, Kremlin Pool Photo via AP)

Before the summit, Mr Putin hailed ties that date to the Soviet army fighting the Japanese military on the Korean Peninsula in the closing moments of the Second World War, and Moscow’s support for Pyongyang during the Korean War.

Mr Kim said relations between Moscow and Pyongyang are now even closer than during Soviet times and called Putin’s visit an opportunity to solidify their “fiery friendship”.

The North Korean leader vowed his country’s “full support and solidarity to the Russian government, army and people in carrying out the special military operation in Ukraine to protect sovereignty, security interests and territorial integrity”. It was not immediately clear what that support might look like.

A big crowd at an official event in Pyongyang
Huge crowds greeted the leaders in Pyongyang (Sputnik, Kremlin Pool Photo via AP)

Mr Kim has used similar language in the past, consistently saying North Korea supports what he describes as a just action to protect Russia’s interests and blaming the crisis on the US-led West’s “hegemonic policy”.

He also hailed Russia’s “important role and mission in preserving the strategic stability and balance in the world”.

Before the talks, Mr Kim welcomed Mr Putin with a lavish ceremony in the city’s main square, where he introduced key members of the North Korean leadership including foreign minister Choe Son Hui; top aide and ruling party secretary Jo Yong Won; and the leader’s powerful sister, Kim Yo Jong.

Huge crowds lined up on the streets to greet Mr Putin’s motorcade, chanting “Welcome Putin” and waving flowers and North Korean and Russian flags.

Mr Putin smiles and puts a hand on Mr Kim's shoulder
The pair hailed their ‘fiery friendship’ and historical ties (Sputnik, Kremlin Pool Photo via AP)

Mr Putin was accompanied by several top officials, including deputy prime minister Denis Mantrurov, defence minister Andrei Belousov and foreign minister Sergey Lavrov, according to his foreign policy adviser, Yuri Ushakov.

US and South Korean officials accuse the North of providing Russia with artillery, missiles and other military equipment for use in Ukraine, possibly in return for key military technologies and aid.

Both Pyongyang and Moscow deny accusations about North Korean weapons transfers, which would violate multiple UN Security Council sanctions that Russia previously endorsed.

Along with China, Russia has provided political cover for Mr Kim’s continuing efforts to advance his nuclear arsenal, repeatedly blocking US-led efforts to impose fresh UN sanctions on the North over its weapons tests.

Mr Putin's boulevard
Mr Putin’s motorcade travels down a main boulevard in Pyongyang (Sputnik, Kremlin Pool Photo via AP)

In March, a Russian veto at the United Nations ended monitoring of UN sanctions against North Korea over its nuclear programme, prompting Western accusations that Moscow is seeking to avoid scrutiny as it buys weapons from Pyongyang for use in Ukraine.

US and South Korean officials have said they are discussing options for a new mechanism for monitoring the North.

South Korean analysts say that Mr Kim will likely seek stronger economic benefits and more advanced military technologies from Russia, although his more sensitive discussions with Mr Putin are not likely to be made public.

While Mr Kim’s military nuclear programme now includes developmental intercontinental ballistic missiles that can potentially reach the US mainland, he may need outside technology help to meaningfully advance his programme.

The two delegations face each other across the table
Mr Putin was joined by senior ministers at the visit (Sputnik, Kremlin Pool Photo via AP)

There are already possible signs that Russia is assisting North Korea with technologies related to space rockets and military reconnaissance satellites, which Mr Kim has described as crucial for monitoring South Korea and enhancing the threat of his nuclear-capable missiles.

The North may also seek to increase labour exports to Russia and other illicit activities to gain foreign currency in defiance of UN Security Council sanctions, according to a recent report by the Institute for National Security Strategy, a think tank run by South Korea’s main spy agency.

There will likely be talks about expanding cooperation in agriculture, fisheries and mining and further promoting Russian tourism to North Korea, the institute said.

In Washington, US secretary of state Antony Blinken said Mr Putin’s visit to North Korea illustrates how Russia tries, “in desperation, to develop and to strengthen relations with countries that can provide it with what it needs to continue the war of aggression that it started against Ukraine”.

Mr Blinken told reporters following a meeting with NATO chief Jens Stoltenberg: “North Korea is providing significant munitions to Russia … and other weapons for use in Ukraine. Iran has been providing weaponry, including drones, that have been used against civilians and civilian infrastructure.”

Tensions on the Korean Peninsula are at their highest point in years, with the pace of both Mr Kim’s weapons tests and combined military exercises involving the United States, South Korea and Japan intensifying in a tit-for-tat cycle.

The Koreas also have engaged in Cold War-style psychological warfare that involved North Korea dropping tonnes of refuse on the South with balloons, and the South broadcasting anti-North Korean propaganda with loudspeakers.

North Korea and the former Soviet Union signed a treaty in 1961, which experts say necessitated Moscow’s military intervention if the North came under an attack.

The deal was discarded after the collapse of the USSR, replaced by a pact in 2000 that offered weaker security assurances. It was not immediately clear if the new deal provides a similar level of protection as the 1961 treaty.