Russian forces are around 3 kilometres (1.9 miles) to the south of the strategically important eastern Ukrainian city of Pokrovsk, open source maps published by Russian and Ukrainian war bloggers show.
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. Ukraine estimates that around 11,000 of them 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 steel industry and vital for the country's pre-war economy - is just a 20-minute drive to the west of Pokrovsk.
An industry source said last week that Ukrainian steelmaker Metinvest BV had halted some of the mine's operations because of the proximity of advancing Russian troops. Its complete closure could more than halve Ukraine's steel output, the country's steelmakers' union has warned. Pokrovsk has hosted since 2014 an important technical university, the largest and oldest in the wider region. Damaged by shelling, it has now suspended its operations.
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 consolidate and advance the front line.
WHAT IS UKRAINE DOING TO DEFEND POKROVSK?
A Ukrainian military official said on Saturday that Ukraine's military leadership had replaced the commander overseeing defences in the Donetsk region where Pokrovsk is located.
General Oleksandr Lutsenko, the outgoing commander, 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 villages and other settlements south of Pokrovsk in recent months 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. 13 showed the facades of apartment blocks badly damaged and a few mostly elderly residents trudging through the streets.
Shell fire could be heard in the distance, "dragon's teeth" anti-tank obstacles had been placed on some roads, and a small shop selling groceries was operating on a power generator.
