Ukrainian forces under intense pressure in key eastern battle

Ukrainian forces are under intense pressure around a strategically important city in eastern Ukraine, where the Russian military has made some of its greatest gains this year, according to the U.K. Ministry of Defense.

Over the last two months Russia has been assaulting heavily fortified Ukrainian positions around Avdiivka, which is situated just a few miles north of Donetsk, the largest Russian-occupied city in eastern Ukraine.

Since the beginning of October Russian forces have advanced by more than a mile, however UK officials claimed the Russian units involved have sustained "thousands of casualties" during that period.

It is impossible for independent journalists to verify the numbers of casualties sustained by either side in the war, however ABC News has verified some videos of the fighting around Avdiivka which appear to show significant numbers of destroyed Russian armored vehicles.

A Ukrainian official confirmed to ABC News that its forces had recently lost control of part of an industrial zone on the edge of the city, but insisted fighting in that area was ongoing.

Control of Avdiivka allows Ukrainian troops to more easily strike Russian transport hubs around the city of Donetsk. However, if the city were to fall to the Russians, Ukrainian transport hubs in the region would become more vulnerable to Russian fire.

Russian forces have encircled Avdiivka from the east, north and south for months, however Ukrainian officials say Russia is now targeting Ukraine's remaining western supply routes in and out of the city.

Harsh winter weather has swept across Ukraine this week and that could slow the Russian offensive down.

Ukrainian and Russian forces continued clashing in and near Avdiivka on Tuesday, according to the Institute for the Study of War.

“Russian sources reiterated claims that Russian forces captured all of the industrial zone southeast of Avdiivka and reached Avdiivka’s southeastern outskirts,” ISW said.

The battle for this eastern city matters officials have said.

Deeply entrenched Ukrainian positions on the outskirts of Avdiivka have withstood nearly a decade of fighting, first in the Donbas war which began in 2014 and then throughout Russia's full-scale invasion which began in February 2022.

If Ukraine was to lose control of the city, it would be a bitter blow to Ukrainian morale.

There is also a giant settlement-sized industrial plant in Avdiivka, which had until May 2022 produced coke, a key ingredient in the steel-making process. Steel is vital for arms production and both side's future ability to produce weaponry may help shape the long-term trajectory of the war.

Ukrainian Tavria Group of Forces Spokesperson Colonel Oleksandr Shtupun said on Tuesday that “Russian forces are attacking in six directions in the Avdiivka area, and that heavy fighting is ongoing near the Avdiivka Coke Plant in northeastern Avdiivka and the industrial zone southeast of Avdiivka."

What's not clear is how long the battle could drag on. Ukrainian troops fiercely resisted a Russian offensive on the eastern city of Bakhmut for about a year, before Moscow captured it.

However Russia is increasingly assertive in the war and the Kremlin seems determined to take Avdiivka at any cost. As it has done to other Ukrainian cities it has captured, Russian is bombarding Avdiivka with artillery and air strikes and reducing the city to a mess of smoldering rubble.

Taking Avdiivka would also open a road for Russians to move on to Pokrovsk, a larger city with thousands of civilians living in it.

Despite the fierce fighting, around 1,300 civilians remain in Avdiivka, according to Ukrainian officials.