Russia's Federal Security Service (FSB) claimed the Main Intelligence Directorate of the Ukrainian Defense Ministry, and its director, Kyrylo Budanov, was behind Saturday's explosion on the Kerch Bridge.
The FSB said on Wednesday it had detained five Russians and three citizens of Ukraine and Armenia over the blast that caused massive damage to the Kerch Bridge that links Russia to Crimea.
Ukraine's interior minister spokesman Andriy Yusov dismissed the allegations as "nonsense."
Dramatic footage of the explosion showed a truck moving across the bridge at the time of the detonation. The bridge was a strategic supply and logistics artery for Russian forces in Ukraine's occupied Kherson region.
Ukraine has not officially confirmed its involvement in the blast, but some Ukrainian officials have celebrated the damage.