Attacks on airfields deep inside Russia will have struck a “powerful psychological blow”, senior Western officials said on Tuesday.
The officials told reporters that Moscow will have to think more carefully about how to keep its long-range bombers safe.
The Engels air base, near the city of Saratov and at least 600 km from the nearest Ukrainian territory, and two other airfields have been hit in the last two days by drone attacks. Ukraine has not claimed responsibility for the attacks but has celebrated them, and Russia retaliated with a “massive strike on Ukraine's military control system”.
The senior Western officials, speaking on condition of anonymity, said the strikes were the deepest inside Russia since its invasion of Ukraine in February.
One of the officials said: “If it were them (the Ukrainians)... it does show that they can operate in Russia at will, and that will deeply worry the Russians. Psychologically I think it strikes a blow.”
The officials said they were confident that Russia kept its strategic long-range bombers at the Engels base, but it would now have to think of moving them.
“It may have the effect of pushing those bombers into dispersed locations,” the official said. “It certainly makes the Russians less confident ... (that) anywhere is safe.”
Russia has used the bombers in its campaign since October to destroy Ukraine's energy grid, signs that, the Western officials said, reflecting Russian president Vladimir Putin’s growing desperation.
Military analysts see the drone strikes on Russia as a response to its attacks on Ukraine’s critical infrastructure.
The Western officials also said Ukrainian claims of an 85 per cent success rate in shooting down Russian missiles were credible, and that Moscow had run out of Iranian drones used to target key energy infrastructure, although a resupply was expected.
“Clearly what we are seeing is a closer partnership between Russia and Iran on the supply of advanced weapons systems, it’s something which concerns us and something we're monitoring very closely,” one of the senior officials said.
Earlier British defence chiefs said Putin’s generals will see attacks on air bases deep inside Russia as the “most strategically significant failures of force protection” in his war against Ukraine.
They believe that the Kremlin’s military top brass will try to blame and punish some officers for the failure to stop the strikes on the Engels Airbase, in Russia’s Saratov province and at Dyagilevo airfield near Ryazan, south-east of Moscow on Monday.
Two Tu-95 BEAR heavy bombers were reportedly damaged at Engels and three people killed when a fuel tank exploded at Dyagilyaevo.
In a briefing the Ministry of Defence in London 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 sites are much deeper inside Russia than previous similar explosions: Engels is over 600km from Ukrainian-controlled territory.”
They added: “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 Russian chain of command will probably seek to identify and impose severe sanctions on Russian officers deemed responsible for allowing the incident.”
Marking Ukraine’s armed forces day, Ukraine’s President Volodymyr Zelensky travelled to the eastern Donetsk region and vowed to push Russian forces out of all of Ukraine’s territory.
He said in a video address to Ukrainian forces from the city of the Sloviansk, a key Ukrainian stronghold in the east: “Everyone sees your strength and your skill.
“I’m grateful to your parents. They raised real heroes.”
