Russian investigators said they believed “explosions” had caused two bridges in the border regions of Kursk and Bryansk to collapse overnight, derailing trains, killing at least seven people and injuring dozens.

In Bryansk, which borders Ukraine, a road bridge collapsed on to a railway line late on Saturday, derailing a passenger train heading to Moscow and killing at least seven people. A rail bridge in neighbouring Kursk also collapsed overnight, derailing a freight train and injuring the driver, officials said. Kursk also borders Ukraine.

State media said Russian investigators were investigating the bridge blasts as “acts of terrorism”. The Kremlin said the Russian president, Vladimir Putin, had been briefed throughout the night.