Two Russian nuclear bombers were reportedly damaged on Monday as media reported explosions air bases in Russia.
The Tu-95 planes - known as Bears - are the only propeller-powered strategic bombers still operational today.
Details were scarce but two servicemen were reported wounded and hospitalised.
Videos showed a huge flash at the high-security airbase in Saratov region used by Vladimir Putin’s strategic fleet.
There were no reports of nuclear contamination.
The early morning blast was reported at the Engels-1 airbase in the Saratov region of Russia. It is around 460 miles from the border with Ukraine.
The Tu-95s have been used for non-nuclear attacks on Ukraine in recent weeks as part of Putin’s blitzkrieg on the infrastructure of his neighbouring country.
Saratov regional governor Roman Busargin said there was no damage to civilian facilities and added that the authorities are checking whether there have been any incidents at military facilities.
Regional media reported sounds of a powerful explosion near the Engels base, and some residents were quoted as saying they saw a flash of light coming from the area.
Asked whether the Russian President has been briefed about the Engels base explosion, Kremlin spokesman Dmitry Peskov said simply that the president is being regularly informed about ongoing developments.
In another unconfirmed incident on Monday, a fuel truck exploded at an airbase near Ryazan, killing three people and wounding six.
A plane was also damaged in the blast at the base, which houses long-range flight tankers that serve to refuel bombers in the air.
The city is a base for Russian special forces troops.
The cause of the Ryazan explosion was not immediately stated.
Firefighters were at the scene.
The explosion was strong and heard at a nearby military camp.
The super-loud Tu-95, known as Bear, first flew 70 years ago.
Putin has deployed the Tu-95s to buzz Britain at moments of high tension, for example in February this year when the Royal Air Force scrambled Typhoon fighters to escort two Bears off northern Scotland.
Ukrainian official Anton Gerashchenko said: “It is from Engels airbase that the [Russian] fascists launch rocket attacks on Ukraine.
“The airfield is located at a distance of 750 km from the border with Ukraine.”
VCHK Telegram channel said the blasts were probably caused by a drone.
“There were explosions at the airfields near Ryazan and Engels [where] there is a strategic aviation airfield.
“There are dead people.
“There was a drone attack in Engels. In Ryazan, it seems, too.”
In Ukraine on Monday, the office of President Volodymyr Zelensky said three rocket strikes hit his hometown of Kryvyi Rih in south-central Ukraine, killing a factory worker and injuring three other people.
In the north-eastern region of Kharkiv, one person was killed in strikes by S-300 missiles on civilian infrastructure in the town of Kupyansk, it said.
The war that began with Russia’s invasion of Ukraine on February 24 has displaced millions from their homes, killed and injured an untold number of civilians, and shaken the world economy - notably through the fallout on the prices and availability of foodstuffs, fertiliser and fuel that are key exports from Ukraine and Russia.
Western countries on Monday began imposing a 60-dollars-per-barrel price cap and a ban on some types of Russian oil, part of new measures aimed at stepping up pressure against Moscow over the war.
The move has prompted a rejection from the Kremlin and also criticism from Mr Zelensky - whose government wants the cap to be half as high.
Russian Deputy Prime Minister Alexander Novak, who is in charge of energy issues, warned in televised comments on Sunday that Russia will not sell its oil to countries that try to apply the price cap.
“We will only sell oil and oil products to the countries that will work with us on market terms, even if we have to reduce output to some extent,” he said in televised remarks hours before the price cap came into effect.
The 27-country European bloc also imposed an embargo on Russian oil shipped by sea.
Russia, the world’s second biggest oil producer, relies on the sale of oil and gas to underpin its economy, which has already come under sweeping international sanctions over Mr Putin’s war in Ukraine.
In recent weeks, Russia has been pounding Ukrainian infrastructure - including power plants - with military strikes and keeping an offensive going in the east, notably in and around the town of Bakhmut.
Russian forces have also been digging in near the southern city of Kherson, which was recaptured by Ukrainian forces last month after an eight-month occupation.
