A truck bomb has caused a fire and the collapse of a section of a bridge linking Russia with Crimea, Russian officials said, damaging a key supply artery for Moscow's faltering war effort in southern Ukraine.
Russian authorities three people were killed in the incident.
A man and a woman who were riding in a vehicle across the bridge were killed by the explosion and their bodies were recovered, Russia’s Investigative Committee said. It did not provide details on the third victim or the truck driver.
The speaker of Crimea's Kremlin-backed regional parliament accused Ukraine, although the Kremlin did not apportion blame.
Ukrainian officials have repeatedly threatened to strike the bridge and some lauded the attack, but Kyiv stopped short of claiming responsibility.
The bombing came a day after Russian President Vladimir Putin turned 70, dealing him a humiliating blow that could lead him to up the ante in his war on Ukraine.
Russia’s National Anti-Terrorism Committee said the truck bomb set alight seven railway carriages carrying fuel, resulting in a "partial collapse of two sections of the bridge".
The Crimean peninsula holds symbolic value for Russia and is key to sustaining its military operations in the south. If the bridge is made inoperable, it would be significantly more challenging to ferry supplies to the peninsula.
While Russia seized the areas north of Crimea early during the invasion and built a land corridor to it along the Sea of Azov, Ukraine is pressing a counteroffensive to reclaim them.
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The bridge has train and road sections. The anti-terrorism committee said the explosion and fire led to the collapse of one of the two links of the road bridge, while another link was intact.
Russia's Energy Ministry said Crimea has enough fuel for 15 days, adding that it was working on ways to replenish stock.
Authorities suspended passenger train traffic across the bridge until further notice.
Mr Putin was informed about the explosion and ordered the creation of a government panel to deal with the emergency.
The 12-mile bridge across the Kerch Strait linking the Black Sea and the Sea of Azov opened in 2018 and is the longest in Europe. It has provided an essential link to the Crimean peninsula, which Russia annexed from Ukraine in 2014.
The £3.2 billion project is a tangible symbol of Moscow's claims on Crimea.
It was Russia's only land link to the peninsula until Russian forces seized more Ukrainian territory on the northern end of the Sea of Azov in heavy fighting, particularly around the city of Mariupol, building a land corridor to Crimea earlier this year.
The speaker of Crimea's Kremlin-backed regional parliament blamed Ukraine for the explosion, but downplayed the severity of the damage and said it would be promptly repaired.
"Now they have something to be proud of: over 23 years of their management, they didn't manage to build anything worthy of attention in Crimea, but they've managed to damage the surface of the Russian bridge," Vladimir Konstantinov, chairman of the State Council of the Republic, wrote on Telegram.
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The parliamentary leader of President Volodymyr Zelensky's party stopped short of claiming that Kyiv was responsible for the incident but appeared to cast it as a consequence of Moscow’s takeover of Crimea and attempts to integrate the peninsula with the Russian mainland.
"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, the leader of the Servant of the People party.
"And this is just the beginning. Of all things, reliable construction is not something Russia is particularly famous for," he added.
Other Ukrainian officials were more celebratory while still stopping short of claiming responsibility.
The secretary of Ukraine's National Security and Defence Council, Oleksiy Danilov, posted a video with Kerch Bridge on fire on the left side and video of Marilyn Monroe singing Happy Birthday, Mr President on the right side.
An adviser to Mr Zelensky, Mykhailo Podolyak tweeted: "Crimea, the bridge, the beginning. Everything illegal must be destroyed, everything stolen must be returned to Ukraine, everything occupied by Russia must be expelled."
In Moscow, Foreign Ministry spokeswoman Maria Zakharova said the "reaction of the Kyiv regime to the destruction of civilian infrastructure shows its terrorist nature".
The blast on the bridge occurred hours after explosions rocked the eastern Ukrainian city of Kharkiv early on Saturday, sending plumes of smoke into the sky and triggering a series of secondary explosions.
The blasts came hours after Russia concentrated attacks in its increasingly troubled invasion of Ukraine on areas it illegally annexed, while the death toll from earlier missile strikes on apartment buildings in the southern city of Zaporizhzhia rose to 17.