Western officials believe Russia could still “win” its war in Ukraine - despite seven weeks of military reversals.
They admitted Vladimir Putin might be able to claim victory, having reset his aims for the conflict - and could even launch a fresh bid to storm the capital.
Forces are fighting in the long-awaited Battle of the Donbas after Kremlin troops began their assault on the breakaway region in eastern Ukraine.
They are thought to be better prepared for the attack than for their initial invasion on February 24 - prompting Ukraine’s allies to send fresh waves of arms and equipment to bolster Ukrainian resistance.
A Western official said tonight: “Putin has clearly failed in meeting his initial, pre-war objectives but he is still in a position to win.”
They added: “The Russians have concentrated sufficient force such that if they were to use it intelligently they might be able to surround and destroy a very significant portion of Ukraine’s armed forces - some of its best forces - and make territorial gains which would then be very difficult to dislodge.
“In a really worst case scenario they may be able to look again at whether they could revisit some of their pre-war objectives, potentially renew an attack on Kyiv or to attempt to take Odesa and deprive the rest of Ukraine from access to the sea.”
“Any one of those things could certainly be described as a success.”
However, Kremlin forces have failed to learn lessons over positioning vehicles in long lines - making them targets for ambushes by Ukrainian fighters.
“They have not solved all of their problems - they continue to operate in relatively long convoys on single roads and make themselves vulnerable and in parallel, the Ukrainians continue to fight in a very smart way,” said an official.
“While we see some improvement, it is as yet not a force transformed.”
Allies are braced to support Ukraine, including by sending weapons, equipment and cash, “for a prolonged period of conflict, through perhaps much of the rest of this year - at least we have to plan for that eventuality”, warned the official.