Ukraine said it blew up a railway bridge in Russia's southwestern Samara region on Monday because it was being used to transport "military cargo".
The incident is the latest in a string of explosions targeting Russia's rail network, which Kyiv says Moscow uses to move troops and equipment for its invasion of Ukraine.
"A railway bridge over the Chapayevka River in Russia's Samara region was blown up. On 4 March 2024, at around 6:00 am (0200 GMT), the bridge was damaged by blowing up its support structures," Ukraine's military intelligence said.
It said Russia was using the railway line to transport ammunition from a plant in the town of Chapayevsk, and that the damage would put it out of service for "a long time".
"An explosive device damaged a pillar on a rail bridge" over the Chapayevka river, Russia's official TASS agency quoted a source in the rescue services as saying.
Traffic on the line was suspended following the attack but later restored, Russian news agencies reported.
Russia's railway operator said "an intervention by non-authorised persons" caused the incident, and that no-one had been injured.
Security services in the region have opened a criminal case into "sabotage", the RIA news agency said.
