Russian troops have infiltrated the strategic city of Kostyantynivka in eastern Ukraine and are now trying to surround it. The entire city is now effectively in a "grey zone", no longer controlled by anyone, Ukrainian soldiers have told the BBC.
"They get into areas behind our backs and in urban conditions it's extremely difficult to push them out," says a Ukrainian drone pilot who operates in that area.
Kostyantynivka is a gateway to the rest of the Donbas region. If it falls, Russian forces would be able to push towards Ukraine's last remaining strongholds in the east, the cities of Kramatorsk and Sloviansk, and move closer to seizing Donbas completely.
Ukrainian commanders claim they have recaptured more territory this year than they have lost, disrupting Moscow's crucial supply lines. On Sunday, Russian-appointed authorities in Crimea suspended fuel sales to the public due to shortages.
But in Kostyantynivka, Russian soldiers have advanced from the south and have even been spotted on the city's northern outskirts. Moscow says its forces are rapidly advancing and have encircled Ukrainian military units.
Brig Gen Oleksandr Bakulin denies this, insisting the situation remains under control and the enemy has no success. However, he acknowledges there are about 130 Russian soldiers still inside the city.
A Ukrainian officer from a unit operating inside Kostyantynivka told the BBC that clean-up and assault groups are still present, but the Russians manage to accumulate more soldiers. Every building acts as a potential shelter.
Russian drone pilots have focused on destroying Ukrainian drone launch sites. The Ukrainian drone pilot says they have limited resources and are often exhausted.
The Ukrainian officer maintains the pace of the Russian advance is very slow: "Sometimes they move 100m a day. Sometimes they even crawl to reach the next building."
Russian forces have adopted a similar strategy to that used in the capture of Pokrovsk, advancing along the flanks to surround the city and cut off supply routes. In recent days, the Russian defence ministry has said it has seized villages to the west of the city.
The Ukrainian drone pilot warns the situation has become a "major crisis". Russian drone units can now use cheap Chinese drones. Delivering supplies has become extremely difficult.
Ukrainian frontline monitoring project DeepState says the fall of Kostyantynivka "is a matter of time". Once that happens, remaining in Kramatorsk will become "extremely dangerous".
Another Ukrainian soldier says they are not getting the necessary reinforcements to cover their losses, and commanders are reluctant to report about lost positions.
Source: www.bbc.com