Surrendering Russian soldiers have switched sides and are now fighting for Ukraine against Vladimir Putin's forces, it is claimed.
Ukrainian officials say a new Freedom of Russia legion has been formed for demoralised troops turning their backs on the Russian invaders.
It comes amid reports of plummeting morale among soldiers fighting the Kremlin's war - with some said to be refusing orders and even shooting down their own planes.
The Russian armed forces personnel have already started training to fight alongside their new comrades, it is claimed.
Pictures purportedly show Russians training alongside their new Ukrainian comrades.
Yesterday the Ukrainian Defence Ministry said on its Telegram channel that commanders have been visiting captured and surrendered Russian troops "in order to select those who wish to serve".
In a follow-up post it said that the "first volunteers" had already started individual additional training.
The ministry stated: "Today the legion's personnel, under the guidance of Ukrainian Armed Forces instructors, studied a NLAW grenade launcher.
"In addition, the commanders of the legion's subdivisions got acquainted with the operational situation on the fronts."
Members of the new legion have "expressed a common desire on behalf of all the volunteers to conduct the first battle against the guard dogs of the Putin regime - the Kadyrovites".
Kadyrovites refers to Chechen fighters loyal to Putin ally Ramzan Kadyrov, who has backed the invasion with troops.
Ukrainian news site Bagnet says that "several hundred" Russians of all ranks had signed up for the legion.
It says that prisoners need to apply in writing, and are vetted by security and counter intelligence services.
It is claimed that more than 17,000 troops Russian troops have been killed since the invasion was launched five weeks ago, with several top-level commanders among the dead.
In a rare public address the head of Britain's GCHQ spy agency said Putin's advisers are scared to tell him the truth about the progress of his Ukraine invasion.
But Sir Jeremy Fleming said the extent of the Russian leader's "misjudgements" must be "crystal clear to the regime".
He said: "It's clear he misjudged the resistance of the Ukrainian people.
"He underestimated the strength of the coalition his actions would galvanise.
"He under-played the economic consequences of the sanctions regime. He over-estimated the abilities of his military to secure a rapid victory.
"We've seen Russian soldiers - short of weapons and morale - refusing to carry out orders, sabotaging their own equipment and even accidentally shooting down their own aircraft.
"And even though we believe Putin's advisers are afraid to tell him the truth, what's going on and the extent of these misjudgements must be crystal clear to the regime."
He added: "It's become his personal war, with the cost being paid by innocent people in Ukraine and increasingly, by ordinary Russians too."
