The Russian president, Vladimir Putin, and the North Korean leader, Kim Jong-un, have signed a pact that includes a clause requiring the countries to come to each other’s aid if either is attacked, a move that has raised western concerns about potential Russian aid for Pyongyang’s missile or nuclear programmes. The inclusion of a mutual defence clause in their comprehensive strategic partnership, which Kim described as an “alliance”, will add to the west’s alarm over growing economic and military ties between North Korea and Russia. The deal was finalised on Wednesday after hours of talks in the North Korean capital, Pyongyang. The pact has also magnified western concerns about potential Russian aid for North Korea’s missile or nuclear programmes. NBC News on Wednesday reported that US intelligence officials believe Putin is providing North Korea with nuclear submarine and ballistic missile technology in exchange for arms for his war in Ukraine. Citing six senior US officials, the US news network said the Biden administration was concerned Russia might help North Korea complete the final steps needed to field its first submarine capable of launching a nuclear-armed missile. It was not immediately clear whether Russian support for ballistic missiles would indicate intercontinental ballistic missiles (ICBMs) capable of reaching the mainland United States, or the short-range ballistic missiles that North Korea has reportedly supplied Russia with during the war and also could use in the event of a large-scale conflict with South Korea. The Nato secretary general, Jens Stoltenberg, said before the summit: “We are of course also concerned about the potential support that Russia provides to North Korea when it comes to supporting their missile and nuclear programmes.” The top US arms control official, undersecretary of state Bonnie Jenkins, has said she believes North Korea is keen to acquire fighter aircraft, surface-to-air missiles, armoured vehicles, ballistic missile production equipment or materials, and other advanced technologies from Russia, Reuters reported. Experts said direct aid for the North Korean regime’s weapons programmes would mark a significant shift in Russian policy since the end of the cold war, driven in part by its battlefield needs in Ukraine. James Acton, co-director of the nuclear policy programme at the Carnegie Endowment for International Peace, said: “The big picture here is how much Russia is re-evaluating its interests about a nuclear-armed North Korea.” Russia may view a nuclear-armed North Korea as a “fait accompli”, he said, and have moved from a policy of grudgingly opposing proliferation alongside the United States to accepting and protecting the regime in return for much needed material aid in its war in Ukraine. Acton said Russia might still not be ready to provide direct support for North Korea’s nuclear programme, and was more likely to aid North Korea’s missile or submarine programmes. Alexander Gabuev, the director of the Carnegie Russia Eurasia Center, said: “What’s significant really is the help for the space programme and the missiles programme if that happens, and that has the direct connection to the nuclear problem. It’s not about the device itself, but about the delivery means. That’s where North Korea will require a lot of expertise and help.” Neither Russia nor North Korea published the text of the security agreement. It was not immediately clear what form that support might take, and few details of the agreement were made public. “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 was quoted as saying by the Russian state news agency, Tass, as he made his first visit to North Korea in 24 years. It is Putin’s second summit with Kim in nine months. Putin later described the pact as “defensive”, citing North Korea’s right to defend itself, Tass reported. He added that Russia would not rule out increasing military-technical cooperation with North Korea. Kim, speaking after the signing ceremony, called the deal the “strongest ever treaty” signed between the two countries, elevating their relationship to the “higher level of an alliance”. The pact would lead to closer political, economic and military cooperation, he said, hailing the agreement as “accelerating the creation of a new multipolar world”. Putin’s visit has been closely watched by the US and South Korea amid concern that growing military cooperation between the isolated, sanctions-hit states could boost the Kremlin’s war effort in Ukraine and add to tensions on the Korean peninsula. In Washington, the US secretary of state, Antony Blinken, said Putin’s visit highlighted Russia’s attempts, “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”. Blinken added: “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.” Last September, during a summit with Putin in Vladivostok, Kim is believed to have agreed to supply missiles and other weaponry for use by Russian forces in Ukraine. In return, Russia would provide food and energy aid and help with North Korea’s space programme. Kim met Putin at Pyongyang’s international airport in the early hours of Wednesday before they were driven through the capital’s brightly lit streets past buildings decorated with Russian flags and portraits of the Russian leader. Hours later, they attended a welcoming ceremony in Kim Il-sung Square, where they saluted a guard of honour and walked across a red carpet to meet important members of Kim’s inner circle, including the foreign minister, Choe Son-hui, and Kim’s influential sister, Kim Yo-jong. Tens of thousands of spectators had packed into the square, including children holding balloons and people wearing coordinated T-shirts in the red, white and blue of the Russian and North Korean flags. Speaking at the start of the talks, Putin thanked Kim for North Korea’s support for his war in Ukraine, calling it part of a wider “fight against the imperialist hegemonistic policies of the US and its satellites against the Russian Federation”. The two leaders exchanged gifts: a luxury Russian-made Aurus limousine and tea set for Kim, and items for Putin that Kremlin aides said were related to his image, “including busts”. Putin later drove Kim through Pyongyang in the Aurus limousine. Gabuev said: “The Russians are looking at every relationship now, since the war is an organising principle of its foreign policy – what can this relationship bring to my battlefield situation in terms of hardware and direct support, what can this relationship bring to my economy that’s in survival mode, and then how can I instrumentalise this relationship to punish the west? “North Korea really checks boxes one and three, and the defence pact is all about that.”