Three people were killed on Saturday in a "truck bombing" at a strategic bridge in Crimea, Russian investigators said.
Russia's Investigative Committee added that the driver of the truck is a resident of Russia's Krasnodar Krai region.
A fire broke out early Saturday morning on the Kerch Bridge -- preceded by an explosion -- causing suspension of traffic and bus and train services.
The Kerch Bridge -- a pair of parallel bridges, a road and a railroad -- is a key supply route for Russia which was built after Crimea's annexation in 2014.
The fire has now been extinguished, Russian authorities said.
Train services to Crimea are expected to resume by Saturday evening, according to Russia's Transport Ministry.
The Russian Anti-Terror Committee said earlier that the bridge was damaged by "a truck bombing."
Footage and images, widely shared on social media, show that a road section collapsed and train carriages were burning on the bridge, which is the longest in Europe.
Thousands of tourists remain stranded in Crimea after the explosion, multiple tour groups said.
'Just the beginning'
Although Ukraine did not directly claim responsibility for the attack, multiple statements by top Ukrainian officials pointed to the possibility.
Crimea is Ukraine, Ukraine's Foreign Ministry said on Twitter.
Ukraine's senior presidential adviser Mykhailo Podolyak said what happened on the bridge is just "the beginning."
"Everything illegal must be destroyed, everything stolen must be returned to Ukraine, everything occupied by Russia must be expelled," Podolyak said in a tweet.
In another cryptic tweet later on Saturday, Podolyak alluded to Russian involvement in the blast.
He claimed the Russian intelligence service FSB or a private military company, likely referring to the Wagner Group, of trying "to eliminate leadership of Defense Ministry/GHQ."
"Before personnel change, FSB is in knockdown — missed Putin's bridge explosion. Defense Ministry can now blame FSB for the future South loss. Isn't it obvious who made an explosion? Truck arrived from RF (Russian Federation)," he wrote on Twitter.
Ukraine's National Security and Defense Council Secretary Oleksiy Danilov shared a video split in two parts, with one side displaying the fire on the bridge and the other side playing Marilyn Monroe's famous "Happy Birthday, Mr. President" song -- a message directed at Russian leader Vladimir Putin, who turned 70 on Friday.
"Putin should be happy. Not everyone gets such an expensive present on their birthday," an anonymous Ukrainian official told the New York Times.
Russia condemned the remarks by Ukrainian officials.
"The reaction of the Kyiv regime to the destruction of civilian infrastructure testifies to its terrorist nature," Russian Foreign Ministry spokeswoman Maria Zakharova said on Telegram.
Russia launched a war in Ukraine on Feb. 24, which has left 6,114 people dead and 9,132 others injured, according to UN estimates.
The war has pushed the world in two camps with Western nations imposing crippling economic sanctions on Russia, and Moscow retaliating by threatening of gas supply cuts to Europe.