Russia has detained eight suspects over the deadly explosion of the bridge linking Crimea to Russia, the FSB security service said in a statement quoted by news agencies.

The suspects include five Russians and "three Ukrainian and Armenian citizens," it said, without providing more details.

"The explosives were hidden in 22 plastic film rolls weighing 22,770 kilograms," it said.

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The rolls were left on a boat in August from the Ukrainian port of Odesa to Bulgaria. They then transited through the port of Poti in Georgia, and were then sent overland to Armenia before arriving by road in Russia, according to the FSB.

The explosives entered Russia on October 4 in a truck with Georgian license plates and reached the region of Krasnodar on October 6, two days before the blasts, the FSB said.

A vital transport link

The "terrorist attack" was organized by Ukrainian secret services, with a Kyiv agent having coordinated the transit of the explosives, according to the FSB.

On Saturday, a blast ripped through the road and rail bridge connecting Crimea to Russia, killing three people, causing damage and igniting a massive fire.

The bridge is logistically crucial for Moscow – a vital transport link for moving military equipment to Russian soldiers fighting in Ukraine. It is also hugely symbolic, with President Vladimir Putin having personally inaugurated the structure in 2018.

The blast sparked celebrations from Ukrainians. 

Russia blamed the explosion on Kyiv on Sunday and launched missile attacks across Ukraine, killing at least 19 people and wounding more than 100, the very next day.

On Monday, Russian President Vladimir Putin said Russia's response to any further Ukrainian attacks would be "severe."