(Updates Dec. 18 explainer with latest battlefield and other

developments)

By Andrew Osborn and Anastasiia Malenko

MOSCOW/KYIV, Jan 14 (Reuters) - Russian forces are

closing in on the strategically important eastern Ukrainian city

of Pokrovsk after capturing a string of villages to its south,

and Ukraine has halted production at its only coking coal mine

nearby due to the advance.

Here are some key points about Pokrovsk and the battle.

WHAT IS POKROVSK?

Pokrovsk is a road and rail hub in Ukraine's eastern Donetsk

region, which had a pre-war population of some 60,000 people.

While most people have fled, Ukraine estimated last month that

up to 11,000 still remain in the city.

It lies on a key road used by the Ukrainian military to

supply other embattled eastern outposts including the towns of

Chasiv Yar and Kostiantynivka in the Donetsk region.

Ukraine's only mine that produces coking coal - used in its

once vast steel industry and vital for the country's pre-war

economy - is just a 20-minute drive to the west of Pokrovsk, and

open source data shows Russian forces are less than 2 km (1.24

miles) from one of the mine shafts.

Two industry sources told Reuters on Monday that

production at the mine had been halted. Its loss could more than

halve Ukraine's steel output, the steelmakers' union has said.

Pokrovsk has since 2014 hosted an important technical

university, the largest and oldest in the wider region. Damaged

by shelling, its windows are now boarded up.

WHY DOES RUSSIA WANT POKROVSK?

Moscow says it has annexed Ukraine's eastern Donetsk region

and sees taking control of Pokrovsk as an important stepping

stone to incorporating the entire region into Russia. Kyiv and

the West reject Russia's territorial claims as illegal and

accuse Moscow of prosecuting a war of colonial conquest.

Control of the city, which the Russian media call "the

gateway to Donetsk", would allow Moscow to severely disrupt

Ukrainian supply lines along the eastern front and boost its

campaign to capture Chasiv Yar, which sits on higher ground

offering potential control of a wider area.

Squeezing the Ukrainian military's access to the road

network in the vicinity would make it harder for Kyiv's troops

to hold pockets of territory either side of Pokrovsk, which

could allow Russia to advance the front line.

WHAT IS UKRAINE DOING TO DEFEND POKROVSK?

A Ukrainian military official said last month that Ukraine's

military leadership had replaced the commander overseeing

defences in the Donetsk region where Pokrovsk is located.

That commander, General Oleksandr Lutsenko, had been

criticised by Ukrainian military bloggers and some lawmakers for

failing to stop Russian troops' relentless push towards

Pokrovsk. He was replaced by General Oleksandr Tarnavskiy.

Oleksandr Syrskyi, Ukraine's top commander, has said his

troops in and around Pokrovsk have prepared for the approaching

Russians by repeatedly strengthening their defensive positions

and he has spoken of sending new reserves, ammunition and

equipment to bolster the defenders.

Russian forces have taken control of villages and

settlements south of Pokrovsk and Ukraine says Moscow has been

throwing everything it has at trying to break through while

sustaining huge losses. Moscow says Ukrainian forces are taking

serious losses. Neither side discloses full casualty figures.

Ukrainian President Volodymyr Zelenskiy visited Pokrovsk in

November where he spoke to troops defending the city and handed

out military awards.

WHAT DOES POKROVSK LOOK LIKE NOW?

The blue and yellow Ukrainian flag continues to fly over

Pokrovsk, but the city is a shadow of its former self, with no

electricity, gas, heating or piped water.

Reuters footage published on Dec. 20 showed the facades

of apartment blocks badly damaged, deserted roads, and some

elderly residents being evacuated along with their cats.

Shell fire could be heard nearby, "dragon's teeth"

anti-tank obstacles had been placed on some roads, and a small

shop selling groceries was operating on a power generator.

Many of those interviewed by Reuters said they refused

to leave because they had nowhere else to go and few financial

resources. Some, like shopkeeper Oksana Yarova, said they had

returned after briefly evacuating earlier in the war.