Overnight into Tuesday a third airfield deep inside Russia came under attack, suffering a fire after an oil storage depot was bombarded by what the Kremlin described as a drone attack that was repelled after the initial blast. A large blaze raged throughout the night as emergency crews responded.

It came the day after two explosions rocked a pair of air bases even further inside Russian territory, which killed three military personnel in the Ryazan region, and Russian Engels-1 airbase in Saratov. Those incidents were also subsequently described by the defense ministry as the result of drone attacks.

The Russian city of Kursk, which lies closer to Ukraine than the other two sites of attack, had thick black smoke rising over its airfield in the early Tuesday hours. "Oil tankers at a base near the city of Kursk, around 60 miles from the border, were on fire and streaming smoke into the sky early Tuesday morning," The Daily Mail writes based on regional sources.

International reports say the large Kursk fire has burned for some ten hours, given a large oil depot was ignited, following the attack:

The inferno covered almost 5,500 square feet and new teams of firefighters were being rushed to the scene, local media said.

Suspected Ukrainian drones also attacked the Belbek military airport in Sevastopol - but were downed by air defenses, say reports.

Increasingly it is looking like Ukraine has made the decision to try and hit much more aggressively inside Russian territory, whether utilizing drones or possibly the longer range missiles being provided by the West, marking a huge escalation. 

"Drones were also targeted at a fuel store in Bryansk region, but failed to cause major damage, said Russian sources," Daily Mail continues.

The Monday attacks had damaged "two nuclear-capable bombers that were thought to be preparing for an attack on Ukraine, killed three ground crew and injured two more."

As for the fresh probable drone attack on the Kursk base, Britain’s ministry of defense said, "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 UK defense official was quoted further as saying, "The Russian chain of command will probably seek to identify and impose severe sanctions on Russian officers deemed responsible for allowing the incident."

So it seems this is Ukraine's response to the widespread aerial attacks on its national energy grid, namely to extend its counteroffensive toward conducting risky cross-border raids on major Russian bases