Sir Jeremy Fleming, who will argue in a speech on Thursday that Vladimir Putin made a "strategic error" in opting to invade Ukraine, claims that Putin's aides are "afraid to tell him the truth" about the conflict.
"We've seen Russian soldiers, who are low on weaponry and morale, refuse to carry out orders, sabotage their own equipment, and even inadvertently shoot down their own planes," the intelligence head will say during a rare public statement during a visit to Australia.
"And, despite the fact that we believe Putin's aides are reluctant to tell him the truth about what's going on and the amount to which it affects him, we believe they are doing so."
“It all adds up to the strategic miscalculation that western leaders warned Putin it would be. It’s become his personal war, with the cost being paid by innocent people in Ukraine and, increasingly, by ordinary Russians too.”
No evidence has been disclosed for the claim Russian troops shot down their own aircraft.
On Wednesday US officials also said Mr Putin is being misled by advisers who were too scared to tell him how badly the war in Ukraine is going and how damaging western sanctions have been.
“We have information that Putin felt misled by the Russian military, which has resulted in persistent tension between Putin and his military leadership,” White House communications director Kate Bedingfield told reporters during a press briefing.
“We believe that Putin is being misinformed by his advisers about how badly the Russian military is performing and how the Russian economy is being crippled by sanctions because his senior advisors are too afraid to tell him the truth,” she said.
Russian forces bombarded areas around Kyiv and Chernihiv just hours after pledging to scale back operations in those zones to promote trust between the two sides, Ukrainian authorities said.
Russian shelling hit homes, shops, libraries, and other civilian areas, they added.
