Three people were killed in a bomb attack on a crucial bridge linking the Crimean peninsula to Russia.
The blast which caused part of the Kerch bridge to collapse was caused by a bomb on a lorry, Russian counter-terrorism authorities said, following the Saturday morning incident.
"According to preliminary information, three people were killed," Russia's investigative committee said. It said they were likely to be "passengers of a car that was near the truck that exploded."
The owner of the lorry believed to have been carrying the bomb has been identified, authorities said.
The bridge is the only one linking Russia to the Crimean peninsula, which Moscow annexed in 2014. The road-and-rail bridge has been a crucial transport link for Russia to send military equipment and reinforcements to troops fighting in Ukraine after President Vladimir Putin ordered his forces to invade the country in February.
Following the blast, Russia's Defence Ministry said that Russian troops fighting in the Mykolaiv, Kryvyi Rih and Zaporizhzhia regions of southern Ukraine could receive all the supplies they needed via existing land and sea corridors.
The explosion sparked a fire on a fuel train on the rail section of the bridge, with photos and videos posted on social media showing flames and black smoke rising from several tankers. Several spans on one side of the road bridge plunged into the water.
"Today at six o'clock seven minutes on the automobile part of the Crimean bridge from the side of the Taman Peninsula, a truck was blown up, which resulted in the ignition of seven fuel tanks of a railway train heading towards the Crimean Peninsula," the Ria Novosti news agency quoted the National Anti-Terrorism Committee as saying.
The explosion comes amid a Ukrainian counter-offensive in the east and south, and days after Mr Putin announced Russia's disputed annexation of four more regions in Ukraine ― Donetsk, Luhansk, Zaporizhzhia and Kherson.
The four territories create a crucial land corridor between Russia and the Crimean peninsula, and together make up about 20 per cent of Ukraine. In recent weeks, Kyiv has retaken vast swathes of land, undermining the Kremlin's claim that it has annexed the four regions because the Russians do not have full control over the areas.
A Kremlin spokesman said Mr Putin had ordered a commission to be set up to look into the blast.
The head of the Russian-installed regional parliament in Crimea, Vladimir Konstantinov, blamed it on "Ukrainian vandals".
There was no immediate official comment from Ukraine.
The fuel train's locomotive and some cars behind were taken to the Kerch railway station in Crimea, Russian state news agency Tass reported.
It said traffic on the bridge was suspended and authorities were working to launch a ferry service. Navigation through the Kerch Strait was not affected, according to an official quoted by the agency.
Mr Putin ordered the construction of the 19-kilometre bridge across the Kerch Strait after annexing the Crimean peninsula in 2014. It was inaugurated in 2018, with the rail section opened a year later.
Russia's annexations have been rejected as illegal by the international community.
Earlier on Saturday, explosions rocked the eastern Ukrainian city of Kharkiv, sending plumes of smoke into the sky and triggering a series of secondary explosions.
Kharkiv Mayor Ihor Terekhov said on Telegram that the early-morning explosions were the result of missile strikes in the centre of the city. He said the blasts sparked fires at one of the city’s medical institutions and a non-residential building. There were no immediate reports of casualties.
Mykhailo Podolyak, an adviser to President Zelenskyy, shared a photo of the burning bridge on Twitter.
"Crimea, the bridge, the beginning," he captioned it. "Everything illegal must be destroyed, everything stolen must be returned to Ukraine, everything occupied by Russia must be expelled."
Russian forces said on Friday they had captured ground in Donetsk in east Ukraine, their first claim of new gains since a Kyiv counter-offensive rattled Moscow's war effort.
The announcement came as Russia's Orthodox leader said President Putin's rule had been mandated by God, congratulating him on his 70th birthday, and as the Nobel Committee awarded the Peace Prize to rights defenders in Russia, Ukraine and Belarus.
Separatist forces in the war-battered Donetsk region said they had retaken a series of villages near the Ukraine-controlled industrial town of Bakhmut, which has been under Russian shelling for weeks.