Explosions have rocked two Russian airbases far from the frontlines as Kyiv appeared to launch a pre-emptive strike on bombers that the Kremlin has used to try to cripple the Ukrainian electrical grid. The Russian defence ministry confirmed the attacks on Monday, claiming two of its warplanes had been damaged when it intercepted two Ukrainian drones. For Kyiv the strike represented an unprecedented operation deep inside Russia to disrupt the Kremlin strategy of provoking a humanitarian catastrophe in Ukraine on the verge of winter. Russian media reports and video posted to social media indicated that an explosion occurred early on Monday morning at the Engels-2 airbase in Russia’s Saratov region, which hosts Tu-95 bombers that have taken part in cruise missile strikes against Ukraine. Another explosion took place at the Dyagilevo military airbase near Ryazan, a city less than 150 miles from Moscow. Three people were killed and five wounded after a fuel truck exploded, Russian state media reported. That base also hosts Tu-95 long-range bombers. Soon after the blasts at the airbases, Russia launched a long anticipated mass strike against Ukraine, involving air-and sea-launched missiles from the Black and Caspian Seas. Ukraine claimed to have shot down 60 of a total of 70 incoming missiles, a new record in the effectiveness of its air defence systems. The Russian defence ministry claimed to have hit 17 targets. In Kyiv, air raid sirens sounded, and people took shelter in underground metro stations, but no missiles hit the capital, and after three hours the all clear was sounded. The strikes plunged some parts of the country into blackout at a time when temperatures are well below zero, but they appeared to have been significantly less successful in disrupting the Ukrainian power grid than the previous Russian mass missile attack on 23 November. Two people in southern Ukraine were said to have been killed and three more wounded after at least one missile slammed into a residential building in Zaporizhzhia. Power was cut in the city of Mykolaiv and Odesa reported disruptions to the city’s water supply. If confirmed as a Ukrainian operation, the strike on the Engels airbase would be the most daring attack behind Russian lines to date. The airbase is a crucial site for Russian air force operations against Ukraine and for the country’s strategic nuclear forces. It has a nuclear weapons storage bunker with warheads that can be deployed on Russia’s long-range strategic bombers. Video of the explosions at the Russian airbases showed a fiery blast illuminating the night sky. Locals reported that the sound of the explosion could be heard from miles away. In one video from Saratov, the sound of an aircraft or missile can be heard screaming overhead shortly before the explosion is heard. Local authorities in the Saratov region said security services were investigating. Baza, a Russian media outlet with sources in the security services, said the Russian airfield at Engels was attacked by a loitering munition, a type of aerial weapon system, which targeted the airbase’s runway. Astra, another independent Russian media outlet, claimed two nuclear-capable Tu-95 bombers were damaged in the explosion. Neither indicated a source for their information. A Ukrainian official offered a cryptic appraisal of Monday’s explosions. “The Earth is round – discovery made by Galileo. Astronomy was not studied in Kremlin, giving preference to court astrologers,” wrote Mykhailo Podolyak, a presidential adviser. “If it was, they would know: if something is launched into other countries’ airspace, sooner or later unknown flying objects will return to departure point.” Among those taking shelter in the Kyiv metro was the UN human rights chief, Volker Türk, who was in Kyiv to meet Ukrainian human rights activists and ended up holding the meeting in a bunker. The Kremlin said Vladimir Putin had been informed of the incidents. The Russian president was reopening the Crimean Bridge on Monday, where an explosion in October raised doubts that Russia could protect the peninsula it had occupied from Ukraine in 2014. Ukrainian monitoring reports in the last week suggested Russia was delivering cruise missiles to the airbase and transferring aircraft to the Ryazan facility in preparation for another attack against Ukraine. Satellite images published by Der Spiegel last week showed 20 strategic bombers parked on the runway at the Engels airbase in preparation for another strike on Ukraine. Satellite images released by Maxar showed those bombers remained parked on the runway through Sunday. Pro-war Russian bloggers have criticised the military for leaving the bombers closely grouped on the runway, making them an attractive target for sabotage or attack. Ukraine is not known to have any loitering munitions that would allow it to attack hundreds of miles beyond the frontlines of the conflict, although there have been reports of such unmanned aerial vehicles under development. As the two military installations were between 300 and 450 miles from the Ukrainian border, Rob Lee, a senior fellow at the US-based Foreign Policy Research Institute, said drones may have been launched by Ukraine from within Russian territory. “The unmanned aerial vehicle attacks have a relatively short range and they would not have been able to fly all that way from Ukraine,” Lee said. The alleged Ukrainian attack on the Engels-2 base was likely to have been aimed at disrupting Russian plans to strike Ukrainian infrastructure, he said. “Ukraine has been warning for weeks now that Russia was preparing for a fresh wave of missile attacks on its energy grid. This could have been a pre-emptive strike.” Russia has resorted to long-range attacks on Ukraine’s energy grid after its troops were forced to retreat from a number of Ukrainian regions after a spirited counteroffensive. Putin called the strikes inevitable after an explosion on the Crimean Bridge that Moscow has blamed on Kyiv. Russia has sustained a number of embarrassing incidents and attacks at military bases, including in occupied Crimea, that have shown the vulnerability of its military.