Two bridges have collapsed overnight in separate incidents in Russian regions bordering Ukraine, killing at least seven people and injuring dozens more.
State media said the collapses were being probed as "acts of terrorism".
A road bridge came down in Bryansk, bringing several heavy trucks onto a moving passenger train late on Saturday, the regional governor said.
At least seven people were killed and at least 71 were injured, Governor Alexander Bogomaz said.
Moscow Interregional Transport Prosecutor's OfficeHours later another bridge collapsed in the Zheleznogorsk district of Kursk, derailing a locomotive train, acting governor Alexander Khinshtein said.
The train caught fire and a driver suffered injuries to his legs, Khinshtein said.
Khinshtein wrote on Telegram in the aftermath: "The cause of the bridge collapse will be established. All emergency services are working on the scene. I am keeping the situation under control."
Moscow Railway alleged on Telegram that the Bryansk bridge came down as a result of "illegal interference".
A Ukrainian national security official said the incidents were Russian "false flag" operations, designed to "manipulate international opinion" ahead of peace talks between Russia and Ukraine in Turkey on Monday.
Andrii Kovalenko, head of Ukraine's National Security and Defence Council's Centre for Countering Disinformation, accused Russia of "laying the groundwork to derail the negotiations".
He added Ukraine had "absolutely no incentive to sabotage the Istanbul summit".
Russian President Vladimir Putin was briefed on the incidents throughout the night, the Kremlin said.
Telegram / Alexander KhinshteiPictures online from Bryansk showed mangled carriages and passengers helping each other climb out of the wreckage in the dark.
Moscow's interregional transport prosecutor's office said an investigation had been launched.
Authorities said the train's locomotive and several cars derailed when the road bridge fell on to it.
Additional emergency workers, as well as rescue equipment and light towers for carrying out work at night have been sent to the area, according to Russian news agency TASS.
The train was going from the town of Klimovo to Moscow and was in the Vygonichsky district when the collapse happened, officials said.
Passengers were evacuated and guided to a meeting point at a nearby station, Moscow Railway said, adding: "They will be able to continue their journey on a specially formed reserve train" travelling from Bryansk to Moscow.
The first incident took place about 100km (62 miles) from the Ukraine border.
Meanwhile, the Ukrainian Air Force said seven regions were hit by intense Russian strikes overnight on Saturday, with a total of 472 UAV and drone attacks and seven missile strikes.
