WATCH: #BNNRussia Reports.

A huge explosion has destroyed part of the Kerch bridge from Russia to Crimea, one of Vladimir Putin’s prestige projects and a vital logistical link for the Russian military. #Ukraine #Russia #War pic.twitter.com/EEWydXuEq9

— Gurbaksh Singh Chahal (@gchahal) October 8, 2022

Authorities say three dead as Russia opens a criminal probe into the blast that blew up the vital bridge linking Moscow-annexed Crimea to the mainland.

A key bridge linking the Crimean peninsula with mainland Russia has been partially destroyed in a truck explosion, Russian media reported, putting at risk a key supply route for Russian soldiers fighting in Ukraine.

The speaker of Russia’s lower house of parliament, the Duma, called it “an act of war” as the country’s investigative committee said on Saturday it had “initiated a criminal case in connection with the incident on the Crimean bridge,” adding that “a truck was blown up”.

“According to preliminary information, this morning on the automobile part of the Crimean bridge from the side of the Taman Peninsula, a truck was blown up, which caused seven fuel tanks to ignite on a train heading towards the Crimea peninsula,” the committee said.

“As a result, two lanes partially collapsed.”

Three people have been found dead so far as the result of the truck explosion, Russia’s Investigative Committee said.

“They are believed to be passengers of a car that was near the truck that exploded. The bodies of two victims, a man and a woman, have already been recovered from the water and their identities are being established,” the committee said in a statement.

The investigators have also established the details of the truck and its owner, registered in Russia’s southern Krasnodar region, and begun searching his place of residence, it added.

Officials said Russian President Vladimir Putin was informed about the explosion and had ordered the creation of a government panel to deal with the emergency.

Ukrainian officials celebrated the incident, but did not claim responsibility, with the head of Ukraine’s National Security and Defence Council, Oleksiy Danilov, posting a video of the burning bridge on social media alongside a video of Marilyn Monroe singing “Happy birthday, Mr President”, a reference to Putin’s 70th birthday on Friday.

Ukrainian presidential advisor Mykhailo Podolyak, meanwhile, suggested late Saturday that Moscow was involved in the blast.

“It is worth noting that the truck that detonated, according to all indications, entered the bridge from the Russian side. So the answers should be sought in Russia,” he said said in comments released by the presidency.

‘A big blow’ to the Russians

Meanwhile, Alexandre Vautravers, the editor-in-chief of Swiss Military Review, cast doubt that a truck was indeed solely behind the explosion, saying a vehicle carrying explosives “is probably not going to produce this much damage” without other explosives being planted on the bridge.

“I think we need to take with a grain of salt the story that is being told to us about how this truck arrived there and all of a sudden produced all of this damage,” he told Al Jazeera.

“The most realistic are two explanations: One would be a laser guided bomb of at least 125 kilos and the other possibility would be sabotage from special forces or from partisans and I think this is something to explore.”

Al Jazeera’s Mohamad Vall, reporting from Moscow, said the explosion represented a “big blow” to the Russians.

“Russians are still trying to make sense of what happened,” Vall said, adding that the bridge is a key supply line between mainland Russia and Crimea.

Reporting from the Ukrainian capital, Kyiv, Al Jazeera’s Rory Challands said there was “jubilation” in Ukraine after the incident.

“This does strike at Vladimir Putin’s prestige. It does strike Vladimir Putin’s image of control. And I think under the bravado of Ukraine at the moment, there might be some nervousness about what his response might be to this,” he added.

“It also gives the Russians a very big headache when it comes to supplying their southern front in Ukraine because the [Russian] army … at the moment is largely supplied by rail networks and that main railway network for the southern front came through Crimea across the Kerch bridge,” Challands said.

He said now the only other route by rail is via the north shore of the Sea of Azov and that is currently about 30 to 40 kilometres from the front lines.

Images shared on social media purported to show fire and damage to the span.

The Tass news agency also reported the fire. Ukraine’s media reported an explosion at the road and rail bridge at about 6am (03:00 GMT).

Putin unveiled the vital road and rail bridge in 2018 after Moscow annexed Crimea from Ukraine in violation of international law in 2014.

Officials in Moscow vowed to find the culprits, but stopped short of immediately blaming Kyiv – though an official in Russian-installed Crimea pointed the finger at “Ukrainian vandals”.

The Russian Defense Ministry, meanwhile, said Russian troops in the south of Ukraine were receiving necessary supplies through the land corridor along the Sea of Azov and by sea. Russia’s Energy Ministry said Crimea has enough fuel for 15 days.

Fighting elsewhere

The fire occurred hours after explosions rocked the eastern Ukrainian city of Kharkiv early on Saturday, sending towering 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 that the blasts sparked fires at one of the city’s medical institutions and a non-residential building. There were no immediate reports of casualties.

In September, Russia announced the annexation of the provinces of Donetsk, Luhansk, Kherson and Zaporizhia after staging referendums that Kyiv and the West say were phoney exercises held at gunpoint.

Ukraine’s military in recent weeks has pushed back against Russian forces across the front lines in the south and the east, including in parts of Donetsk. Western weaponry has helped the Ukrainian army win back more territory in the past month than Russian forces have taken in five months.

On Saturday, Putin announced that Air Force General Sergei Surovikin would take overall charge of the invasion of Ukraine, representing the first time one military leader has been appointed to oversee the entire effort, which Moscow has dubbed a “special military operation”.