Huge explosions tore through two oil storage facilities in a Russian city near the border with Ukraine this morning after suspected drone strikes by Ukrainian forces.

The blasts occurred within 15 minutes of each other in Bryansk, about 95 miles from Ukraine, Russian state television said, without speculating on their causes. It said one of the explosions was at a fuel tank at a military base, the other at a nearby oil refinery owned by Transneft, the state-controlled oil company.

Video showed two massive fires burning a short distance from each other. Black smoke could be seen billowing from the military base, while an inferno engulfed the Druzhba refinery. Bryansk is a key transit point for Russian troops heading to Ukraine.

The explosions occurred at about 2am, according to Russia’s emergencies ministry. No casualties were reported. A railway line that transported Russian military equipment to Ukraine was also damaged in a separate blast, according to unconfirmed reports.

Analysts said that Bryansk, with a population of about 400,000 people, was in range of Ukrainian Tochka-U missiles and that the facilities could have been targeted by Kyiv to hinder the supply of fuel to invading Russian forces. The two storage depots contained a combined total of 15,000 tones of oil, Russian media said.

Rob Lee, of the Department of War Studies at King’s College London, posted a video of the fires and the explosion. “It sounds like this was an air or missile strike,” he said. “Most likely, a Tochka-U tactical ballistic missile, which has the range to reach both targets if they are deployed close to the Ukrainian-Russian border.”

Baza, a Russian media outlet that has sources within the security services, said, however, that investigators believed the depots were targeted by combat drones. Analysts said Ukraine may have used Turkish-produced Bayraktar drones to carry out the strikes. The governor of the neighbouring Kursk region said today that the Russian military had destroyed two military drones. State media later published images of fragments of Bayraktar drones that it said had been discovered by a local woman.

If confirmed as Ukrainian strikes, the explosions would represent arguably the most significant attack on Russian territory by a foreign army since the end of the Second World War. Russia has warned that it will launch missiles at government buildings in Kyiv in response to any Ukrainian strikes on its territory.

Security officials in Ukraine have warned that Moscow is planning to stage “false flag” attacks in an effort to justify an escalation of the conflict.

Ukraine has not commented on suspicions that it targeted the facilities in Bryansk. A number of schools near the burning depots were evacuated this morning and locals said that private vehicles were being stopped from entering the city. Several Russian border regions have raised their terrorist threat levels since the start of the invasion.

“You could believe in one accidental fire, but two at the same time? Of course not,” said Ivan Zhdanov, an exiled ally of Alexei Navalny, the imprisoned Kremlin critic. “The war has crossed over into Russia and is already impossible to ignore.”

Separately, blasts were also reported in the capital of Moldova’s pro-Russian breakaway region of Transnistria, which shares a border with western Ukraine.

Officials from the breakaway region said its interior ministry building had been fired on by unknown assailants with a grenade launcher, although this was not confirmed.

Broadcast footage showed the windows and doors blown out. Fire crews were shown at the scene. There were no immediate reports of casualties.

Rustam Minnekayev, deputy commander of Russia’s central military district, has been quoted by Russian state news agencies as saying that full control over southern Ukraine would give it access to Transnistria, which has been a disputed territory occupied by Russian military forces since the fall of the Soviet Union.

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Ukraine previously warned that Russia might stage false flag operations in the territory.

In Moscow, the deputy foreign minister Andrei Rudenko appeared to play down Minnekayev’s remarks, saying Russia saw no risks in Transnistria, and wants a peaceful settlement there, Interfax news agency reported.

Last week Moscow accused Ukrainian combat helicopters of attacking a village in the Bryansk region, injuring seven people. Officials have also blamed Ukraine for an attack on a fuel depot in the Belgorod border region. Kyiv denied it was involved. Seventeen people were killed last week in a huge fire that erupted at a key Russian defence research institute in Tver, north of Moscow, while a chemical plant in central Russia caught fire. Moscow has blamed the blaze in Tver on faulty wiring.

Five Russian military recruitment offices have been set on fire by anti-war activists since the start of the invasion of Ukraine, opposition media has reported. Suspects in three of the arson attacks reportedly told police they wanted to disrupt any mobilisation. A 21-year-old man suspected of throwing a petrol bomb at a recruitment office near Moscow is said to have jumped out of a window and escaped while police officers were distracted.

The blasts in Bryansk came as President Putin said Russian FSB security agents had arrested a group of neo-Nazis who were planning to kill a prominent Russian journalist. Putin, 69, said the plot was orchestrated by Ukraine with assistance from the CIA. “They have switched to terror [tactics,]” he said.

Shortly after Putin’s comments, Tass reported that members of a far-right terrorist group called National Socialism/White Power had been arrested in Moscow. Investigators said they were planning to assassinate Vladimir Solovyov, a pro-Kremlin television presenter who has been sanctioned by western countries.

Putin also accused western countries of trying to destroy Russia from within, as well as trying to discredit the Russian army through media outlets and social media. “Their efforts will fail,” he said at a meeting with the country’s top prosecutors.

Although Russia has shifted its attention from Kyiv towards the Donbas region of eastern Ukraine, it has yet to make a “significant breakthrough”, Whitehall has said. The Ministry of Defence in London said in an intelligence update that Putin’s forces lacked “sufficient logistical and combat support enablers” and had made only “minor advances” in the region.

Ukrainian forces are continuing to hold out in the encircled Azovstal steel plant in the besieged city of Mariupol after weeks of fighting. Putin instructed his defence chief last week to blockade the industrial plant and to call off plans to storm the sprawling facility.

The Institute for the Study of War, a US think tank, said Ukrainian sources had reported that Moscow may be preparing for “renewed assaults” on the facility, which would “likely lead to high Russian casualties”.

The MoD suggested that Russia’s failure to take Mariupol swiftly had hampered their ability to carry out operations elsewhere. Its update on Monday said that Russia’s decision to besiege rather than attack Mariupol’s Azovstal steel plant meant many Russian units “remain fixed in the city and cannot be redeployed”. It is thought that a Russian victory in the city would free up as many as 6,000 of Russia’s forces for operations in Donbas.