In a major blow for Russian President Vladimir Putin, a huge explosion has severely damaged the only bridge connecting the annexed Crimean peninsula with the Russian mainland, paralyzing a key supply route for Moscow’s faltering war in Ukraine.

The blast early Saturday caused parts of the Kerch Strait road and rail bridge — opened by Putin himself in 2018 — to collapse, images and video from the scene showed. At least three people were killed in the explosion, Russian officials said, citing preliminary information.

The exact cause of the blast at Europe’s longest bridge is yet to be confirmed. Russian officials said a truck exploded, causing Crimea-bound sections of the road part of the bridge to collapse. A subsequent fire engulfed a train of fuel tanks on a separate, adjacent rail portion of the bridge.

Putin ordered a “government commission” to examine the Kerch bridge “emergency” in Crimea, Russian state media TASS reported.

An official in Crimea blamed “Ukrainian vandals” for the explosion. Some Ukrainian officials gloated over the incident without directly claiming responsibility. Russian Foreign Ministry spokeswoman Maria Zakharova said that “the reaction of the Kyiv regime to the destruction of civilian infrastructure testifies to its terrorist nature.”

The damage to the road bridge appears to be severe, with the part of the bridge that carries westbound road traffic crippled in at least two places. The damage to the rail link where fuel tanks caught fire is unclear.

The bridge is strategically important because it links Russia’s Krasnodar region with the Crimean peninsula, which was annexed by Russia from Ukraine in 2014 in a move condemned by the international community.

It is a critical artery for supplying Crimea with both its daily needs and supplies for the military. Over the last few months, dozens of Russian military convoys have used the bridge, carrying vehicles, armor and fuel.

If the Russian military can’t use the bridge, its supply lines to forces in southern Ukraine would become more tenuous, especially when combined with Ukrainian advances southwards into Kherson region, north of Crimea.

Russia has used the Crimean railroads to ferry supplies to forces in Kherson, and several rail hubs in both Crimea and Kherson have been attacked by long-range Ukrainian rockets.

Sergey Aksenov, the Russian-appointed Head of Crimea, said “two spans of the roadbed of the part [of the bridge] from Krasnodar to Kerch, collapsed” after the explosion, and that a train’s fuel tanks caught fire.

Video and images from the 19-kilometer (11-mile) bridge appear to show a portion of the roadway had fallen into the water below, with several charred rail fuel tanks remaining on the adjacent track.

“As soon as the fire is extinguished, it will be possible to assess the extent of damage to the bridge and pillars, and it will be possible to talk about the timing of the restoration of traffic,” Aksenov said.

Russia’s Investigative Committee said on Telegram that preliminary information indicates three people were killed in the incident, “presumably the passengers of a car that was next to the blown-up truck.”

At least two bodies, that of a man and a woman, were recovered from the water, and their identities were being established, the investigative panel said.

Records indicate the truck that exploded belonged to someone in Russia’s Krasnodar region; investigators are checking the owner’s home and trying to determine the truck’s route, the investigative committee said.

The bridge spans the Kerch Strait, which connects the Black Sea to the Sea of Azov, on which sit key Ukrainian ports, including Mariupol. For Russia, the bridge symbolizes the physical “reunification” of Crimea with the Russian mainland.

No further details on the timing or scope of the commission have been announced.

Russian state media RIA Novosti said that there are “no projections for the timing of the restoration of the Crimean bridge yet,” citing Putin’s press secretary Dmitry Peskov.

An official in Crimea placed blame on “Ukrainian vandals.”

“Ukrainian vandals somehow managed to get their bloody paws on the Crimean bridge. And now they have something to be proud of, in 23 years of their economic activity, they did not manage to build anything deserving of interest in Crimea. But they did succeed in damaging the roadbed of the Russian bridge,” Chairman of the State Council of the Republic of Crimea Vladimir Konstantinov said.

“Such is the whole essence of the Kiev regime and the Ukrainian state … Of course, the causes of the accident will be investigated, and the damage will be repaired swiftly,” he added.

CNN cannot independently verify Konstantinov’s claim.

Ukraine reacts to explosion

Ukrainian officials taunted Russia over the explosion without directly acknowledging that Ukraine was responsible for the attack.

“Air defense of the Russian Federation, are you sleeping?” the Navy of the Armed Forces of Ukraine said on Facebook, alongside a video showing a section of the bridge’s road that had been completely destroyed.

“Russian illegal construction is starting to collapse and catch fire. The reason is simple: if you build something explosive, sooner or later, it will explode. And this is just the beginning,” David Arakhamia, the head of Ukrainian president Volodymyr Zelensky’s party in parliament and a member of Kyiv’s negotiating team with Russia, said in a Telegram statement about the incident.

A senior Ukrainian official, Oleksiy Danilov, posted video of the damaged Kerch bridge alongside a clip of Marilyn Monroe singing “Happy Birthday, Mr President,” which Monroe performed for President John F. Kennedy in 1962. Putin turned 70 on Friday.

On Thursday, Oleksii Hromov, a senior official with the General Staff, said that since September 21, Ukrainian troops had managed to advance 55 kilometers in the north-east, “establish control over 93 settlements, [and] take control over more than 2,400 square kilometers.”

Hromov appeared to be referencing gains in Kharkiv region that were made before September 21 but only confirmed later.

“In the Kherson direction, the enemy is trying to counter-attack at the expense of reserves in order to restrain the advance of our troops and regain lost positions. Since October 1, 29 settlements have been taken under [our] control,” he said.

In an interview in August, a senior Ukrainian military commander said the Kerch bridge was a legitimate target.

“This is a necessary measure in order to deprive them (Russia) of the opportunity to provide reserves and reinforce their troops from Russian territory,” Maj. Gen. Dmytro Marchenko said in an interview with RBC-Ukraine.

Russia’s bridge to Crimea

The Kerch bridge is able to handle 40,000 cars a day and to move 14 million passengers and 13 million tons of cargo per year, state news agency RIA Novosti reported when Putin opened the bridge in 2018.

Russian special forces masked in camouflage without unit insignia seized Crimea in a lightning operation in February 2014. Initially, Russia denied that its troops had carried out the mission. Later, it acknowledged that the so-called “little green men” were indeed Russian units. The West responded swiftly with crippling economic sanctions.

After the bridge opened, the United States condemned its construction as illegal.

“Russia’s construction of the bridge serves as a reminder of Russia’s ongoing willingness to flout international law,” according to a US State Department statement at the time.

“The bridge represents not only an attempt by Russia to solidify its unlawful seizure and its occupation of Crimea, but also impedes navigation by limiting the size of ships that can transit the Kerch Strait, the only path to reach Ukraine’s territorial waters in the Sea of Azov.”

Ukrainian officials echoed those sentiments following the explosion.

“Crimea, the bridge, the beginning. Everything illegal must be destroyed, everything stolen must be returned to Ukraine, everything occupied by Russia must be expelled,” Mykhailo Podoliak, who is an adviser to Ukraine’s leader.

Train hit in eastern Ukraine

Meanwhile, a cargo train in Ilovaisk in the Russian-occupied Donetsk region was hit by a “powerful explosion” Saturday morning, according to the adviser to Mariupol Mayor Petro Andrushenko.

“Not only Crimea. Not only fuel tanks. There is also a cargo train in Ilovaisk. Locals report a rather powerful explosion and subsequent detonation at night. The occupiers now have big problems with supplies from both sides,” Andrushenko said.

Pro-Russian authorities in the self-declared republic of Donetsk confirmed the cargo train incident, releasing video Saturday showing the fire’s aftermath at a local railway station.

Russia’s Ministry of Emergency Situations said on Telegram that shelling “by Ukrainian militants” caused the fire. CNN cannot independently verify the claim.

On Thursday, US President Joe Biden expressed caution about the dangers stemming from Putin’s nuclear threats as his military continued to experience military setbacks in Ukraine.

“First time since the Cuban missile crisis, we have a direct threat of the use (of a) nuclear weapon if in fact things continue down the path they are going,” Biden warned Thursday evening during remarks at a Democratic fundraiser in New York.

He added: “I don’t think there’s any such thing as the ability to easily (use) a tactical nuclear weapon and not end up with Armageddon.”