Explosions caused two bridges to collapse overnight in Russian regions bordering Ukraine, Russian officials said Sunday without specifying what caused the blasts. 

Russia’s Investigative Committee said it would be investigating the incidents as potential acts of terrorism.

The blasts, which came ahead of peace talks scheduled for Monday in Istanbul, killed at least seven people and injured dozens more.

In Russia’s Bryansk region, an explosion caused a road bridge to collapse onto a railway line late Saturday, derailing a passenger train heading to Moscow, according to the Russian authorities. A separate rail bridge in the neighboring Kursk region was blown up hours later in the early hours of Sunday, derailing a freight train and injuring the driver, the authorities said.

The Investigative Committee, the country’s top criminal investigation agency, said in a statement that explosions had caused the two bridges to collapse, but did not give further details. Several hours later, it edited the statement, which was posted on social media, to remove the word “explosions” but did not provide an explanation, the Associated Press reported.

In the Bryansk region, social media pictures and videos showed part of a passenger train crushed under a collapsed road bridge. “The bridge was blown up while the Klimovo-Moscow train was passing through with 388 passengers on board,” Alexander Bogomaz, the region’s governor, told Russian television.

Acting Kursk Governor Alexander Khinshtein, meanwhile, wrote on Telegram that a bridge collapsed in his region’s Zheleznogorsky district while a freight train was moving, injuring one of its drivers.