A Russian freight train derailed on Monday in the western region of Bryansk bordering Ukraine after an "explosive device" detonated on the tracks but there were no casualties, the local governor said.
Officials said power lines had been blown up in northern Russia, which the FSB security service called an "act of sabotage".
The apparent attacks came a day after a Ukrainian strike killed four people in a Russian village in the Bryansk region and as Kyiv prepared for a widely expected counter-offensive.
"An unidentified explosive device went off, as a result of which a locomotive of a freight train derailed," Bryansk governor Alexander Bogomaz said on Telegram.
There were no casualties, he said.
He said emergency services were working at the scene and that rail traffic in the area had been suspended.
There have been reports of sabotage on railroads in Russia and its ally Belarus throughout Moscow's more than year-long Ukraine offensive.
But this was the first time Russian officials confirmed an attack of this scale.
Footage on social media showed the front of the train and several cargo carriages on fire and lying on the grass next to the tracks.
Russian Railways said the incident took place on Monday at 10.17am local time between the town of Unecha and the village of Rassukha in the south-western corner of region – some 100km from the Ukrainian border.
It said the front locomotive and seven wagons derailed "after the intervention of unauthorised persons."
"As a result of the incident, the locomotive caught fire," it said in a statement.
It later said that the fire had been put out by midday and that passengers of two Moscow-bound trains in the area would be taken by bus to the regional capital Bryansk.
Earlier on Monday, the governor of the northern Leningrad region, Alexander Drozdenko, said local power lines had been blown up by an "explosive device".
The official said the lines were damaged near the village of Susanino, 60km south of Russia's second city Saint Petersburg and posted images of the lines lying on the ground in a forest.
Drozdenko later said the FSB security service had opened a criminal case on "sabotage".
Russian strikes
Russian missile attacks across Ukraine wounded 34 people in the central Dnipropetrovsk region on Monday, including children, regional authorities said .
The barrage followed another wave of attacks last week that ended a weeks-long pause after systematic Russian strikes targeting key infrastructure.
"There are already 34 wounded due to a missile attack on the Pavlograd district," Sergiy Lysak, the head of the Dnipropetrovsk region, said on social media.
"Five of them are children. The youngest is a girl and only eight years old," Lysak said.
Ukraine said Russia attacked at around 2.30am, adding it had downed 15 out of the 18 missiles launched by Moscow's forces.
The Russian defence ministry meanwhile said it had launched long-range precision strikes on Ukrainian ammunition production facilities.
"All assigned facilities were hit," the defence ministry said in a statement.
Ukraine has strengthened its air defences, including with US Patriot systems after it appealed to Western allies to help fend off Russian attacks on the energy grid.
Ukrainian officials also said on Monday that Russian forces had killed one person and wounded three others in the southern Kherson region within the past 24 hours.
Russia still controls part of the Black Sea region, having withdrawn from the eponymous regional capital last November.
Most of the fighting in Ukraine in recent weeks has centered on the eastern Donbas region, particularly the city of Bakhmut.
Russia has been posting slow incremental gains in the industrial town and controls some 80% of it.
The commander of Ukraine's ground forces, Oleksandr Syrsky said Monday that his troops had led small counter-attacks in the now-destroyed city.
"In certain parts of the city, the enemy was counter-attacked by our units, and left some positions," he said.
Russia is "failing to take control of the city," Syrsky said, adding that the situation was still "quite complicated."
AFP