Air bases deep within Russian territory have been hit by a string of mysterious explosions in the latest humiliating blow for President Vladimir Putin.

Footage has emerged of blasts on Monday at the Engels-2 air base in the Saratov region, as well as the Dyagilevo military air base near Ryazan, just 80km from the Russian capital.

Three people were killed in the Ryazan attack and several injured, while two Tu-95 BEAR heavy bombers were reportedly damaged at Engels.

A day later, a third drone strike hit a Russian airfield in Kursk, leading to dramatic scenes after an oil tanker caught fire in the blast.

So far, there has been no explanation regarding who carried out the attacks, although it is widely assumed that Ukraine was responsible.

Russia has also pointed the finger at Ukraine, sparking fears it could cause a dramatic escalation in the war if Russia were to retaliate aggressively.

It is also not yet known exactly how the attacks happened, leading to speculation Kyiv may have secretly developed a new weapon, potentially a modified drone or long-range rocket.

However, one thing that experts do agree on is just how significant the latest developments are in the war that has already dragged out for nine agonising months.

According to the UK’s Defence Ministry, the explosions at the Russian air bases may be “some of the most strategically significant failures” since the war began.

“The causes of the explosions have not yet been confirmed. However, if Russia assesses the incidents were deliberate attacks, it will probably consider them as some of the most strategically significant failures of force protection since its invasion of Ukraine,” the ministry stated in a tweet.

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“The sites are much deeper inside Russia than previous similar explosions: Engels is over 600km from Ukrainian-controlled territory.

“Engels is the main operating base of Russia’s Long Range Aviation (LRA) within western Russia and is home to more than 30 heavy bombers.

“These aircraft contribute to Russia’s nuclear deterrent and have also frequently been used to launch conventional cruise missiles at Ukraine.”

The ministry predicted that the LRA was likely to respond by “temporarily moving bombers to dispersal airfields” – and that the repercussions could be brutal.

“The Russian chain of command will probably seek to identify and impose several sanctions on Russian officers deemed responsible for allowing the incident,” it concluded.

Meanwhile, Johann Sollgruber, the European Commission’s Former Head of Representation of EU in Austria, said the attacks proved Ukrainian efforts to “develop long-range combat drones”, while Anton Gerashchenko, an adviser to the Ukrainian interior ministry, added that the Engels airfield was “one of the most important bases of Russian air forces”.

“Two regiments of strategic bombers are stationed here which are part of Russia’s aerial nuclear deterrence tactics. Planes can be seen on Google Earth,” he tweeted.

And it comes amid growing speculation that Russia’s supplies of Iranian-supplied kamikaze drones had been exhausted, after The Guardian reported an unnamed Western official said Russia had “run out” of the drones around a fortnight ago, and was currently “anticipating a resupply”.

If all this is true, and Ukraine has managed to develop long-range weapons at the same time as its enemy has run out, then it leaves Russia more vulnerable than ever before, opening up the possibility of even more attacks deep within the Russian border – and greater revolt from a Russian population growing increasingly frustrated by Putin’s military failures.