Between 20,000 and 30,000 Russian troops have been killed and wounded in the battle for the Ukrainian city of Bakhmut since it began last summer, Western officials say. The epic nature of the battle is out of all proportion to Bakhmut's strategic significance, they add. But after more than six months of grinding, horrific fighting, the future of Bakhmut still hangs in the balance. Since the fighting began, some 90% of its pre-invasion population has fled.