An explosion has derailed a freight train for the second day in a row in a Russian region bordering Ukraine, sending both the locomotive and some cars off the tracks, authorities said.
Russian territory and Crimea, annexed by Moscow in 2014, have been hit in recent days by a series of attacks.
The last four days have seen two trains derailed by explosions, a suspected drone hitting an oil depot in Crimea that caused a huge blaze and power lines blown up near Saint Petersburg.
The strikes come as Russia gears up to celebrate May 9, a holiday marking the Soviet victory over the Nazis that has become a central event during President Vladimir Putin's rule.
Ukraine followed its usual line of not claiming responsibility for the attacks, which came as Kyiv said it was finalising preparations for a spring offensive announced weeks ago.
Alexander Bogomaz, the governor of Russia's western Bryansk region, said on Tuesday the train was derailed by an "unidentified explosive device".
He said it went off at Snezhetskaya station, outside the regional hub of Bryansk, a city of around 370,000 people near the Ukraine and Belarus borders.
"A locomotive and several wagons of the train derailed," he said, adding that there were no casualties.
Tass news agency, citing law enforcement agencies, said firefighters were working at the scene and two recovery trains had been dispatched to the area.
Local prosecutors had begun an investigation into the derailment, it added.
Pictures of that incident shared on social media showed several tank carriages lying on their side and dark grey smoke billowing into the air.
Rail sabotage
On Monday, a similar explosion caused a train to derail and catch fire near Unecha, in the same region but closer to the Ukraine border.
Throughout its more-than-year-long offensive, the Kremlin has sought to portray Russia as safe while its troops fight in Ukraine.
Earlier on Tuesday, it acknowledged a security threat.
"Of course, we are aware that the Kyiv regime, which is behind a number of such attacks — terrorist attacks — plans to continue this line," Kremlin spokesman Dmitry Peskov said.
"All our intelligence services are doing everything necessary to ensure security."
Russian Railways also put out a statement saying the train had derailed due to "the intervention of unauthorised persons in the work of rail transport".
It did not mention an explosive device.
The state operator said the incident took place at 7:47pm local time between Snezhetskaya and the nearby village of Belye Berega.
It said the train's front locomotive and "around 20 wagons" were derailed and that rail traffic in that section had been suspended.
There have been many reports of sabotage on railways in Russia since Moscow launched its Ukraine offensive, but this week is the first time officials confirmed attacks.
More than 65 people, a third of which were minors, have been detained in recent months in around 20 regions of the country on charges of railway sabotage, according to a count by the independent media Mediazona published in mid-April.
US to send Ukraine $450 million in 37th military aid package
The US is sending Ukraine about $US300 million ($450 million) in additional military aid, including an enormous amount of artillery rounds, howitzers, air-to-ground rockets and ammunition, US officials said on Tuesday.
The new package includes Hydra-70 rockets, which are unguided rockets that are fired from aircraft.
It also includes an undisclosed number of rockets for the High Mobility Artillery Rocket Systems, or HIMARS, mortars, howitzer rounds, missiles and Carl Gustaf anti-tank rifles.
The weapons will all be pulled from Pentagon stocks so they can go quickly to the front lines. The officials spoke on condition of anonymity because the aid has not yet been formally announced.
The latest shipment comes as Ukrainian officials say they are readying a counteroffensive — with Ukrainian Defence Minister Oleksiy Reznikov declaring they are in the "home stretch, when we can say: 'Yes, everything is ready'".
Ukrainian officials have said they were stockpiling ammunition to stow it along potentially long supply lines.
Mr Reznikov said on Monday that the key things for the assault's success would be "the availability of weapons; prepared, trained people; our defenders and defenders who know their plan at their level, as well as providing this offensive with all the necessary things — shells, ammunition, fuel, protection, etc."
This is the 37th package of Pentagon stocks to go to Ukraine since the war began in February 2022, and it brings the total US military aid to about $US36 billion ($54 billion).
Denmark meanwhile said it was sending 1.7 billion kroner ($375 million) worth of military aid to Ukraine to support the forthcoming Ukrainian offensive.
The package included mine clearing vehicles, ammunition and financial support for the procurement of air defence, the Danish defence ministry said in a statement.
"The equipment … is essential to pave the way for Ukrainian tanks and mechanised infantry on the front line," Acting Defence Minister Troels Lund Poulsen said.
ABC/wires
