In the nearly two weeks since Vladimir Putin annexed Ukraine’s Kherson and Zaporizhzhia regions in a lavish ceremony in the Kremlin, Russia’s forces have been retreating there, outmanned and outgunned.

They now face a far greater struggle to supply their front lines after an explosion ripped through the crucial bridge connecting the annexed peninsula of Crimea to the Russian mainland early on Saturday.

The apparent attack sent two of the Kerch Bridge’s road spans crashing into the sea and set a nearby railway shipment of fuel tanks ablaze, halting all traffic on the route which the Russian military relies on to ship supplies and equipment into the war zone in southern Ukraine.

It was a deeply personal humiliation for Russia’s president, who opened the $3bn, 12-mile infrastructure link by driving a Kamaz truck over it in 2018.

Built to cement Russia’s 2014 annexation of the peninsula, the smouldering bridge has overnight become a symbol of Russia’s struggle to cope with the Ukrainian advance in the south-east.

Michael Kofman, a military analyst and director in the Russia Studies Program at CNA, a US defence think-tank, said the loss of the rail link would “substantially constrain Russian ability to move troops and supplies through Crimea, until they are able to repair it”.

The only other supply route is through recently annexed territory in south-eastern Ukraine. But the so-called “land bridge” that Russia has created by annexing four regions is difficult to traverse. Rail lines are few and far between, mostly single-track, and must cross bridges over rivers and irrigation canals flowing to Crimea and the Azov and Black Seas.

Ukrainian missile strikes on railway infrastructure had already significantly limited Russia’s ability to resupply forces across the south by land. Russia has also lost significant numbers of trucks during the invasion.

“It’s going to be very hard for them to make it up any other way. They really have to move heaven and earth to get that railway line reopened,” , said Phillips O’Brien, professor of strategic studies at the University of St Andrews.

The disruption could help Ukraine to expand its counteroffensive and try to retake the annexed regions from Russia, O’Brien added.

The Russians are “in real, real trouble”, he said. “The Russian army is in bad shape. Morale is not great. Supply is not great. The Ukrainian army is really large and really well-trained now and combat-ready. It’s hard to see the balance going more towards them than it is now.”

Ukraine’s hopes of retaking the peninsula were widely seen as a pipe dream for years, even in Kyiv, but now seem less fanciful as its troops press their advantage on the ground.

Though Ukraine has not taken credit for them, the attack on the bridge is the latest in a daring series of strikes on military infrastructure in the peninsula and elsewhere behind enemy lines.

These have gradually chipped away at Russians’ sense of normalcy which accompanied Putin’s 2014 annexation and the first six months of Moscow’s “special military operation,” a term evoking far-off conflicts in places like Syria rather than the brutal reality of war on Russians’ doorsteps.

After Ukraine routed Russia’s forces in the eastern Kharkiv region in September, Putin shattered that domestic illusion by mobilising the army’s reserves, moving to annex the four regions and threatening to use nuclear weapons to defend them.

But that escalation has spectacularly backfired. Some 100,000 Russians have fled to Kazakhstan to avoid the draft — as many as joined the army — while Ukraine’s steady advance through territories Putin claims are part of Russia has undermined his own willingness to defend them.

The exact circumstances of the Kerch Bridge attack remain unclear. Russia claims a truck was packed with explosives, despite passing an inspection on the mainland minutes earlier, and accused Ukraine of terrorism.

Ukrainian officials gleefully celebrated the blast but have not confirmed Kyiv’s involvement, while casting suspicion on Moscow’s version of events and suggesting it could be part of security forces’ infighting in the blame game for Russia’s failures.

The Kremlin has allowed Russia’s army to face withering public criticism in state media and from some officials in recent days as they search for a scapegoat for the battlefield failures.

Ardent supporters of the war have called on Putin to escalate further by destroying Ukraine’s critical infrastructure.

“We’re already villains for the western world. So let’s scare them rather than be a laughing stock,” Vladimir Soloviev, one of Russia’s most prominent state television commentators, wrote on social media app Telegram. “Ukraine must be plunged into the Dark Ages. Bridges, dams, railways, power stations, and other such infrastructure objects must be destroyed.”

The cause of the explosion “doesn’t matter as much as the net result”, said Mykola Bielieskov, an analyst at the National Institute for Strategic Studies in Kyiv.

Russia will probably be forced to rely on the limited stocks of weapons, ammunition and other military supplies it already has on the peninsula to supply the front in mainland Ukraine over the next several days or even weeks, Bielieskov said. That means it may need to be cautious about the rate of expenditure of materiel as Ukraine’s rolling counteroffensive presses south.

The Kremlin attempted to project a sense of calm, saying Putin ordered an investigation into the incident but had no plans to address the Russian people.

Within hours, authorities said they were reopening the bridge to road and rail traffic, assuring locals in Crimea that supplies of food and petrol would continue and projecting implicit assurances Russia could still supply the front in Ukraine. Marat Khusnullin, Russia’s deputy prime minister for construction and regional development, toured the damaged bridge after nightfall and oversaw a test ride with a multi-car freight train, the state-run RIA news agency reported.

“Striking the bridge was considered one of the red lines that could bring about the worst-case scenario: a furious reaction up to and including nuclear retaliation,” Tatiana Stanovaya, founder of political consultancy R. Politik, wrote on Telegram.

But “experience shows us that Putin always gets around to reacting to military setbacks very belatedly . . . and swallows them — instead of striking back, he more often pretends that nothing really happened”, she added.

Russia’s capacity to retaliate is limited by its own poor battlefield performance and failure to establish air superiority, O’Brien said.

“They’re having to do it from standaway missiles because they’re afraid to fly over Ukraine. But it just doesn’t seem they’re accurate enough, and the Ukrainians are good at intercepting enough of them that they can’t do it.”

Letter in response to this article:

Who benefits from these mysterious explosions? / From Sir Anthony Brenton, Cambridge, UK