Russia’s Federal Security Service (FSB) said it has arrested eight “accomplices” in its ongoing investigation into the Saturday bombing attack on the Kerch bridge in annexed Crimea.

“So far, five Russian nationals, as well as three Ukrainians and Armenians who took part in preparations for the attack have been arrested as part of a criminal case,” the FSB announced, according to Russian state news outlet TASS.

Russian officials say the attack was carried out through an explosive device concealed in rolls of polyethylene film and placed inside a cargo truck. The cargo—which consisted of twenty-two pallets weighing over 22,000 kilograms—was allegedly delivered by sea from Odessa to Bulgaria, then to Georgia, Armenia, and back to Georgia before making its way to Russia through the Upper Lars border crossing. The cargo’s illicit contents were reportedly laundered at several points throughout the trip using falsified registration and destination documents. FSB officials claim the cargo’s movements were coordinated by an officer of the Main Directorate of Intelligence of the Ministry of Defence of Ukraine.

Maj. Gen. Nikolai Vdovin told Russian news outlet RIA Novosti that the cargo was likely outfitted with “sensors” capable of counteracting radars and other equipment intended to detect explosives.

The FSB claimed the bombing was masterminded by the head of Ukrainian military intelligence (GUR), Kyrylo Budanov. Russian authorities identified at least twelve “accomplices”—including three Ukrainians and an Armenian—eight of whom have allegedly been arrested. Russian political commentators have speculated that the FSB report could lead to internal purges, suggesting that an operation of this scale could not have been properly executed but for the betrayal or extreme negligence of multiple Russian officials.

The bridge attack, which killed three people and temporarily halted both train and car traffic, was followed by an unprecedented barrage of Russian missile and drone strikes against critical infrastructure targets across Ukraine. “It is obvious that the Ukrainian secret services ordered, organized, and carried out” the Crimea bridge attack, Russian president Vladimir Putin said on Monday. “If attempts continue to carry out terror attacks on our territory, Russia’s responses will be tough and by their scope correspond to the level of threats created for the Russian Federation … no one must have any doubts about that.”

The FSB’s allegations were dismissed as “nonsense” by GRU press secretary Andriy Yusov. “All the activities of the FSB [...] are nonsense. They are fake structures serving Putin’s regime, so we definitely will not comment on their statements,” Yusov said on Wednesday. Though the attack was celebrated by the Ukrainian public and some officials in Kyiv, the Ukrainian government has so far not formally taken responsibility for the Crimea bridge bombing.

Mark Episkopos is a national security reporter for the National Interest.

Image: Reuters.