After more than seven months of war, Jeremy Fleming, director of the GCHQ spy agency, told BBC Radio that Russia was running short of munitions, friends and troops.
Russian President Vladimir Putin has so far stayed within established military doctrine of not using nuclear weapons, Fleming said, but his agency would be looking out for signs that this could change.
Register now for FREE unlimited access to Reuters.com Register"I would hope that we will see indicators if they started to go down that path," he said, without saying what those indicators could be.
"They're seeing just how badly Putin has misjudged the situation," he will say, according to excerpts from his speech.
Register now for FREE unlimited access to Reuters.com RegisterReporting by Sachin Ravikumar, Kylie MacLellan, Kate Holton, Michael Holden and Elizabeth Piper, Editing by Andrew CawthorneOur Standards: The Thomson Reuters Trust Principles.