The head of MI6, who will step down in September after five years in the role, used an outgoing speech to say the Russian president is “stringing us along” amid faltering efforts to broker a truce.
Moscow has continued to pound Ukraine with attacks in recent weeks and peace appears no closer despite months of Washington-led talks.
Speaking at the British consulate in Istanbul on Friday, Sir Richard said there was “absolutely no evidence” that the Russian leader wants to settle the conflict as he seeks to “impose his imperial will by all means at his disposal”
“But he cannot succeed,” Sir Richard said.
“Bluntly, Putin has bitten off more than he can chew. He thought he was going to win an easy victory. But he – and many others – underestimated the Ukrainians.”
