Shipping operations are reported to have been stopped after explosions hit the Kerch bridge linking mainland Russia to the annexed Crimea region.
Ukraine’s navy and security service (SBU) carried out a “special operation” using seaborne drones, an SBU source told AFP.
Two people were killed and their daughter was injured in an “emergency” on the bridge, Russian authorities said.
The road was damaged near the Crimean end of the bridge, Russia’s Ministry of Transport added.
Security company Ambrey reported two explosions in the early hours of Monday within 16 minutes of each other.
Several videos of the damaged bridge were circulated on social media, showing a partial collapse of the road, and other parts splitting apart, leaving integral load-bearing metal rods bare. The rail section remained undamaged.
Road traffic was halted, while rail services were likely to be disrupted.
Ferry operations running parallel to the bridge were halted, Ambrey said.
The company observed that no merchant vessel had transited the Kerch Strait since about four hours prior to the explosions.
Vessel traffic had not resumed by midday.
Initial reports had indicated that the bridge was attacked by Ukrainian unmanned surface vessels.
The bridge was damaged by Ukrainian sabotage acts once before, disrupting traffic for eight months by the time Russian authorities declared the rail and roadway fully reopened.
The attacks came hours before Moscow pulled out of a deal to keep Ukrainian grain flowing on bulkers from the Black Sea.
That move, however, had been anticipated well before the bridge attacks, and Russian presidency spokesman Dmitry Peskov denied any link between the two developments.