Eight people have been detained over Saturday's blast that damaged the only bridge connecting annexed Crimea with the Russian mainland, marking a critical juncture in Moscow's invasion of Ukraine.

Russia's Federal Security Service (FSB) claimed the main intelligence department of the Ukraine's Ministry of Defence, its head Kyrylo Budanov, and its employees and agents organized the "terrorist attack" on the Kerch Strait road-and-rail bridge, Russian state media RIA Novosti reported Wednesday.

"At the moment, five citizens of Russia, three citizens of Ukraine and Armenia, who participated in the preparation of the crime, have been detained as part of a criminal case," the report by FSB and the Russian Investigative Committee said, according to RIA Novosti.

"The explosive device was concealed in rolls with polyethylene construction film on 22 pallets with a total weight of 22,770 kilograms," the FSB report added, RIA Novosti also reported.

Ukraine has yet to publicly comment on the new claims by Russia's FSB and Investigative Committee.

The over the weekend served as a major blow to what the Kremlin calls its "special military campaign" in Ukraine, as Moscow counters among Russian troops and .

The bridge is strategically important because it links Russia's Krasnodar region with the Crimean peninsula, which Russia annexed from Ukraine in 2014 in a move roundly criticized by the international community.

It is a critical artery for supplying Crimea with both its daily needs and supplies for the military. Over the last few months, dozens of Russian military convoys have used the bridge, carrying vehicles, armor and fuel.

Limited car and rail traffic has restarted on the bridge following the blast. However, larger vehicles like heavy trucks, vans and buses are travelling by ferry.

Russian officials had earlier claimed the explosion was caused by a truck blowing up on the road bridge. The report said the explosive device had been sent from the port of Odesa in early August this year through Bulgaria, Georgia and Armenia, Russian state media TASS reported.

The blast also sparked a feverish response , which used the explosion to justify a wave of across Ukraine Monday in scenes that echoed the early days of the invasion.

At least 19 people and more than 100 injured during the attacks, which targeted across Kyiv and other major Ukrainian cities, according to Ukrainian officials.

Russian President Vladimir Putin later threatened further responses that correspond "to the level of threat to the Russian Federation, have no doubt about it," while accusing Kyiv of "terrorism."

Earlier, Ukrainian officials had gloated over the bridge blast but did not claim responsibility for the attack.