The Ukrainian fighters did a “very successful job of taking down” the Russians in the Lysychansk region before retreating, an intelligence expert told Sky News.
Lysychansk is the last remaining major city in the eastern region of Luhansk under Ukrainians control is now under Russian control.
Former British military intelligence officer Forbes McKenzie said it was not important for the Ukrainians to keep control of Lysychansk to win the war.
He said: “They quietly moved out of Lysychansk over the weekend. It wasn’t broadcast that they were going to do that.
“They’ve done a very successful job in reducing Russian in that area. Lysychansk wasn’t the key – they didn’t have to own the city to win the war.
“What they did was very successful taking down the Russians and then they withdrew.
“There is a road going from Slovyansk to Bakhmut. It is estimated that the Ukrainians will move to the west of that road, where they will dig and prepare for the next attack.”
‘Forecast of attacks to the north’
Mr. McKenzie said the next phase will determine the actions of the Russians.
He added: “The Russians we see are carrying out exploratory attacks to the north.
“We see the activity going on from the Russians now that will set the conditions for what they can do next.
“But I think it’s worth mentioning that the Russians are weakening. They have a real problem with force generation.
“The Chief of Defense Staff (UK) Patrick Saunders talks about the amount of bombs and ammunition that will be fired in 48 hours, which could deplete a typical NATO country.
“A lot is happening and a lot needs to happen for the next phase.”
However, he said any ambition for the Ukrainians to retake Lysychansk would “need troops on the ground and a lot of effort”.
The UK Ministry of Defense’s latest intelligence report says fighting in and around the Luhansk region has “intensified” over the past week.
It added that with withdrawal of Ukrainian troops from LysychanskRussia “almost certainly” will move to capture the Donetsk region.