Russia’s Black Sea flagship vessel, the Admiral Makarov, was damaged and possibly disabled during an audacious Ukrainian drone attack over the weekend on the Crimean port of Sevastopol, according to an examination of video footage. Open-source investigators said the frigate was one of three Russian ships to have been hit on Saturday. A swarm of drones – some flying in the air, others skimming rapidly along the water – struck Russia’s navy at 4.20 am. Video from one of the sea drones shows the unmanned vehicle weaving between enemy boats. Ukrainian officials said it was unclear if the Admiral Makarov was badly crippled, or had escaped with light damage. Unconfirmed reports said its hull was breached and radar systems smashed. Social media recorded loud explosions in the southern part of Sevastopol, in an area known as Riflemen’s Bay. A Russian navy school is located nearby. The ministry of defence in Moscow said Ukraine used nine air and seven sea drones, several of which were intercepted, including by a Russian helicopter. It made no mention of the Admiral Makarov. The ministry admitted there was “minor damage” to a minesweeper, the Ivan Golubets. On Sunday, Moscow said the drones had been recovered and were being analysed. The ministry said they were equipped with Canadian-made navigation modules. It blamed the UK for the attack and said a Royal Navy unit masterminded operations from the southern Ukrainian port of Ochakiv. The UK government has dismissed this. A Ukrainian journalist, Andriy Tsaplienko, shared dramatic footage shot by a drone in action off the Crimea coast in which it appeared to dodge bullets hitting the water on its way to a target ship. He said the Admiral Makarov was damaged along with at least two other ships that carry Kalibr cruise missiles, including a transport vessel – either the Chamois or Lightning. “There is a good chance that several ships are not just damaged but sunk,” he wrote. On Sunday GeoConfirmed, a volunteer group, said an “Admiral Grigorovich-class frigate” was a victim of the attack. After examining stills photos, it concluded: “Only the Admiral Makarov matches this class for the Black Sea Fleet.” The video stops when a drone reaches the Russian boat, it added, with the unmanned vessel “likely” blowing up on impact. Aides to Ukraine’s president, Volodymyr Zelenskiy, have hinted the country was behind the well-orchestrated raid on Saturday. His government has not claimed responsibility. This is the second time Kyiv appears to have punched a hole in a prestigious Russian naval vessel, in a carefully planned operation that caught the Kremlin off-guard. It follows the dramatic sinking in April of the Moskva battleship, a Soviet-built gun platform with a crew of 510. Many perished. That was the first time Russia had lost a flagship since the 1905 Russo-Japanese war, with the Moskva the largest vessel to be sunk in conflict since 1945. Russia’s entire Black Sea fleet now looks vulnerable to remote warfare. Andriy Zagorodnyuk, Ukraine’s former defence minister, described Saturday’s strike as “an interesting development”. “Whoever did it employed a group attack. It’s not like a single rocket hitting a target. It’s coordinated. A number of air and sea drones overload the Russian defence system. If you shoot one or two down, others get through,” he told the Guardian. “This is a swarm tactic.” Zagorodnyuk said he was struck by the fact the drones had “a quite powerful live video connection”. They were able to record the attack, despite the fact they were in operation more than 100 miles from the Ukrainian coast. “That this can be done over this distance is remarkable,” he observed. By contrast, the Iranian kamikaze drones that attacked Kyiv two weeks ago were more primitive and “flew blind”, he noted. Ukraine has shown it is able to strike at long-distance targets in Crimea, which Russia annexed in 2014. It is presumed to have struck the bridge connecting the peninsula with Russia, the Saky aerodrome, and – two months ago – the naval headquarters building in Sevastopol. Zelenskiy has vowed to liberate Crimea, together with all of occupied southern and eastern Ukraine. In the wake of the Sevastopol attack the Kremlin said it was pulling out of a UN-brokered grain deal that allows civilian ships to export grain and fertiliser from Black Sea ports. Zelenskiy, however, said Moscow was looking for a pretext to end the initiative. It had been “deliberately aggravating” the food crisis since September, he said in a video address. Russia’s actions had effectively blocked the passage of ships, he added, with 176 vessels stuck in the agreed grain corridor, some waiting for “more than three weeks”. They were unable to deliver their cargo to countries such as Algeria, Egypt, Yemen, Bangladesh and Vietnam, he said. Zelenskiy stressed: “A strong international response is needed now. Both at the UN level and at other levels. In particular, at the level of the G20. Ukraine has been and can continue to be one of the guarantors of global food security. Russian terror and blackmail must lose. Humanity must win.” Ukraine’s foreign minister, Dmytro Kuleba, said Moscow had taken the decision to “resume its hunger games long ago and now tries to justify it”. He tweeted: “By suspending its participation in the grain deal on a false pretext of explosions 220km away from the grain corridor, Russia blocks 2m tonnes of grain — enough to feed over 7 million people.” The UN secretary-general, António Guterres, said he was “deeply concerned” about the end of the deal. He delayed his travel to Algiers for the Arab League Summit by a day to focus on the issue, a UN spokesperson said on Sunday. Guterres was engaged in “intense contacts” to get the agreement back and spoke with the EU’s top diplomat, Josep Borrell.