The Russian President Vladimir Putin has made a huge error as he is “running out of troops” because they are getting “thinner and thinner” because they are being left behind to garrison captured towns.

The director of the Royal United Services Institute (Rusi) Professor Michael Clarke has said that Russian troops who are left behind to guard captured towns are being hit with fierce opposition affecting the Kremlin’s push to advance.

Professor Clarke told Sky News, “The problem that the Russians have is if you’re invading a country that doesn’t want you there, every time you capture somewhere, you’ve got to leave troops behind, you’re protected.

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“So the troops at the front of the push get thinner and thinner.

“So the push gets harder the further away you are from your base.

“At some point, the Russians will start to run out of troops strange as it may seem.”

Asked how long he thinks it will be before Ukraine capital is totally surrounded, he replied, “Well, it’s hard to tell, they’ve made very hard work of it so far.

“But we have to expect that in the next let’s guess three-four days, Kyiv will probably be surrounded and then the next phase of this fairly awful war will begin to unfold”