A firefighter helicopter pours water on fire on a collapsed part of the Kerch Strait bridge in Crimea, 08 October 2022. According to Russian authorities, "an explosion was set off at a cargo vehicle on the motorway part of the Crimean bridge on the side of the Taman peninsula, which set fire to seven fuel tanks of a train that was en route to the Crimean peninsula. Two motorway sections of the bridge partially collapsed." EPA-EFE/STRINGER 
The FSB said the explosion was organised Ukrainian military intelligence and its director, Kyrylo Budanov. The explosive device was moved from Ukraine to Russia via Bulgaria, Georgia and Armenia, the FSB said.
The FSB, which is the main successor to the Soviet-era KGB, also said that it had prevented Ukrainian attacks in both Moscow and the western Russian city of Bryansk.
Ukraine has not officially confirmed its involvement in the bridge blast, but some Ukrainian officials have celebrated the damage.
The explosion on the twelve mile-long bridge destroyed one section of the road bridge, temporarily halting road traffic. It also destroyed several fuel tankers on a train heading towards the annexed peninsula from neighbouring southern Russia.
The bridge, a prestige project personally opened by Russian President Vladimir Putin in 2018, had become logistically vital to his military campaign, with supplies to Russian troops fighting in south Ukraine channelled through it.
Russian forces launched mass missile strikes against Ukrainian cities, including power supplies. At a televised meeting of Russia's Security Council on Monday, Putin said the strikes were a retaliation for the Crimea bridge blast, which he said had been organised by Ukraine's secret services.
(Reporting by Reuters; editing by Guy Faulconbridge)