Russian air bases have faced deadly drone attacks thought to be carried out by Ukraine.
The UK Defense Ministry said these attacks could mark the worst force protection failures of the war.
The attacks occurred hundreds of miles into Russia territory, far from the front lines.
Drone attacks on Russian air bases - far from the front lines in the Ukraine war - could be viewed by Moscow as the most glaring force protection failure since the invasion of Ukraine was launched in late February, the British Ministry of Defense said.
"The causes of the explosions have not 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 British defense ministry said Tuesday, adding that "the Russian chain of command will probably seek to identify and impose severe sanctions on Russian officers deemed responsible for allowing the incident."
Two air bases in Russia were attacked on Monday in incidents that were followed by a drone strike on Tuesday at an oil facility near an airfield in Kursk - located on the border with Ukraine. Monday's drone strikes occurred at Engels-2 air base in Saratov, roughly 315 miles from Ukrainian territory, and the Dyagilevo air base in Ryazan, approximately 285 miles from Ukrainian territory and roughly 130 miles from Moscow. The airbases house Russian strategic bombers.
Three Russian military personnel were killed in the attacks on Monday, and aircraft were also damaged, Moscow said. Ukraine has not claimed responsibility, but Russia blamed Monday's attacks on Kyiv.
"The Kyiv regime, in order to disable Russian long-range aircraft, made attempts to strike with Soviet-made unmanned jet aerial vehicles at the military airfields Dyagilevo, in the Ryazan region, and Engels, in the Saratov region," the Russian defense ministry said, per Reuters.
Russia fired yet another barrage of missiles at energy infrastructure across Ukraine on Monday,
Mikhail Podolyak, an advisor to Ukrainian President Volodymyr Zelenskyy, in a cryptic tweet said that the Kremlin should know "if something is launched into other countries' airspace, sooner or later unknown flying objects will return to departure point."
The drones involved in attacks on two Russian bases on Monday were launched from Ukrainian territory, the New York Times reported, citing a senior Ukrainian. The official also told the Times that special forces aided in at least one of the strikes.
"Ukrainian forces likely conducted strikes on two Russian strategic airbases on December 5, inflicting light damage while demonstrating Ukraine's ability to strike Russian rear areas and possibly disrupt Russia's campaign of strikes against Ukrainian infrastructure," according to an assessment from the Institute for the Study of War (ISW), which has closely tracked the conflict in Ukraine.
"Ukrainian forces likely sought to disrupt Russian strikes against Ukrainian critical infrastructure and demonstrate Ukraine's ability to target Russian strategic assets," ISW added.
Ukraine has largely avoided striking targets within Russia since the war began, excluding Ukrainian territory that Russia illegally annexed. The attacks on Russian air bases seemingly mark a new chapter in the conflict.
Samuel Bendett, a military expert with the Center for Naval Analysis, a Washington think tank, told Insider that Russia's inability to protect its airbases is "baffling."
"Why didn't Russian air defenses track and identify the targets so deep inside the country?" Bendett said in discussions with Insider's Charles Davis.
Mick Ryan, a retired major general in the Australian Army, tweeted that the drone attacks were a "a psychological strike against Russia."
"This attack on a military target deep in Russia will cause consternation among a public who thought they were safely insulated from the war," Ryan added. His comments reflect Ukraine's stated aspirations with previous attacks in Russian-occupied Crimea - bringing the war closer to the Russian people.