On Saturday, a truck bomb exploded, causing a fire and the collapse of a section of a bridge connecting Russia-annexed Crimea with mainland Russia, which has been vital for Moscow's supply in southern Ukraine.
The bridge attack comes a day after Russian President Vladimir Putin turns 70.
According to Russia's National Anti-Terrorism Committee (NATC), the truck bomb set fire to seven railway cars carrying fuel, causing a "partial collapse of two sections of the bridge." However, the committee did not blame anyone right away.
The Crimean Peninsula has symbolic significance for Russia and is critical to the country's military operations in the south. If the bridge remains inoperable, transporting supplies to the Crimean Peninsula will be much more difficult.
Earlier, Russia took control of the areas north of Crimea early in the invasion and built a land corridor to it along the Sea of Azov. Ukraine is waging a counteroffensive to reclaim them.
The bridge has both train and automobile lanes. According to Russia's NATC, the explosion and fire caused the collapse of two sections of one of the two links of the automobile bridge, while another link remained intact.
Commuter train traffic across the bridge has been halted until further notice. Putin was informed of the explosion and directed the formation of a government panel to handle the situation.
The 19-kilometre Kerch Strait bridge connecting the Black Sea and the Sea of Azov is Europe's longest bridge. It has served as a vital link to Crimea, which Russia annexed from Ukraine in 2014. Ukrainian officials have threatened to destroy the bridge on numerous occasions.
In May 2018, Russia opened the first section of the bridge to car traffic. The parallel rail bridge opened the following year.
This USD 3.6 billion project is a physical manifestation of Moscow's claims to Crimea. It was Russia's only land link to the peninsula until Russian forces seized more Ukrainian territory on the northern end of the Sea of Azov earlier this year in heavy fighting, particularly around Mariupol.
In August, Russia was hit by explosions at an airbase and munitions depot in Crimea, highlighting the country's vulnerability.
The truck bombing on the bridge happened hours after explosions rocked the eastern Ukrainian city of Kharkiv early Saturday, sending towering plumes of smoke into the sky and setting off a chain reaction of secondary explosions.
The explosions occurred just hours after Russia focused its increasingly troubled invasion of Ukraine on areas it had illegally annexed. At the same time, the death toll from earlier missile strikes on apartment buildings in the southern city of Zaporizhzhia rose to 14.
On Wednesday, Putin signed documents claiming four regions of Ukraine as Russian territory, including the Zaporizhzhia region, which is home to Europe's largest nuclear power plant, the reactors of which were shut down last month.
That move was foreshadowed by Russia's annexation of Crimea in March 2014, which Moscow claimed was carried out after residents of the peninsula voted to join Russia. This action was widely condemned, prompting sanctions from the United States and the European Union.