An explosion has crippled the heavily guarded bridge connecting Crimea to the Russian mainland, a hated symbol of Russian occupation and key logistics link for Russian troops in southern Ukraine, in the latest heavy blow to Vladimir Putin after weeks of military humiliation. The Kerch bridge was a personal prestige project for the Russian president, and the hit came the day after his 70th birthday. The blast destroyed the road into Crimea and left the railway link in flames. Ukraine did not directly claim responsibility for the attack, which Russia said was carried out by a truck bomb. But one senior Ukrainian official posted a “happy birthday” message with images of destruction, and the country’s post office revealed – within hours – designs for a commemorative stamp, showing the bridge ablaze, raising questions about whether the explosion had been anticipated. The leader of President Zelenskiy’s political party also suggested the attack was a consequence of Russia’s illegal occupation of Crimea. “Russian illegal construction is starting to fall apart and catch fire. The reason is simple: if you build something explosive, then sooner or later it will explode,” wrote David Arakhamia, head of the Servant of the People party, on Telegram. Moscow had claimed the Kerch crossing was virtually untouchable – protected by layers of defences from trained military dolphins to the latest missile systems – making the attack particularly damaging. If it was planned in Kyiv, it would be the latest sign of Ukrainian military confidence on the ground, even as Russia claims more Ukrainian territory on paper. No serious military analyst is suggesting that Ukraine is close to being in a position to regain Crimea, but the idea feels much less fanciful than it did a year ago. However, Russia has threatened retaliation for any attack on the bridge. Celebrations in Ukraine about the damage – which is likely to make it harder for supplies and reinforcements to reach occupying troops in the south – were mixed with concern about a possible escalation. Putin has warned that he is prepared to use nuclear weapons, as his troops struggle to halt a Ukrainian counteroffensive that has left them in disarray. On Friday, Zelenskiy, in an interview with the BBC, said Russian officials had begun to “prepare their society” for the possible use of nuclear weapons. “They begin to prepare their society. That’s very dangerous. They are not ready to do it, to use it. But they begin to communicate. They don’t know whether they’ll use or not use it. I think it’s dangerous to even speak about it.” By Saturday evening, Russia said the rail link across the bridge was operational again but road traffic would remain constricted. Hours after the explosion, Russia announced it had appointed a notorious veteran with a bloody record as its first overall commander for the war in Ukraine. Sergei Surovikin opened fire on pro-democracy protesters in the 1990s and led the 2017 Russian military expedition in Syria, where he was accused of using contentious tactics, including indiscriminate bombing of anti-government fighters. His appointment may indicate that Moscow now understands that its military is in danger of collapse in Ukraine, with Kyiv’s forces advancing in all four of the southern regions that Putin claims to have annexed. The explosion on the bridge, which witnesses said could be heard miles away, happened at about 6am on Saturday while a train was crossing; it was engulfed in flames and sections of the road bridge collapsed into the water. Russia set up a committee to investigate the attack. Within hours it said three people had been killed and blamed a truck bomb for the blast. It said the driver was a resident of the southern Russian Kuban region. Footage shared on Russian Telegram channels and news agencies appeared to show the moment of the explosion, with two vehicles, a truck and a car, at the centre of the blast, although it was unclear whether either was responsible or simply caught up in the detonation. The bridge, which was built on Putin’s orders and inaugurated in 2018, was a key transport link for military equipment to Russian soldiers fighting in Ukraine, especially in the south, as well as ferrying troops there. Russia had for months assumed that Crimea – including the Kerch bridge – was beyond the ability of Ukrainian forces to strike. However, in the past two months a series of explosions have hit sites in the Crimea, including the Saky naval airbase, amid mounting confidence in Kyiv that it can retake Crimea. On Friday, Ukrainian officials also warned about a crisis at the Zaporizhizhia nuclear plant, Europe’s largest, where weeks of fighting have repeatedly damaged power lines that run cooling systems for reactors. Overnight shelling once again cut power to the plant, and Petro Kotin, head of the state nuclear company Energoatom, warned that the plant had only limited diesel to fuel emergency backup generators. “Right now we are working on logistics to supply more fuel for these generators,” Kotin told BBC World News. “If [the generators] run out of fuel, after that they will stop, and after that there will be a disaster … there will be a melting of the active core and a release of radioactivity from there.”