In a Friday intelligence update, Britain reported that Ukrainian troops were forced to retreat from certain areas in the battle city of Bakhmut after Russia renewed its assault with heavy artillery in the last two days.

The report said that the Russian MoD, and the Wagner Group had improved their co-operation. It was referring to the Russian defence ministry and the main mercenary group.

The British military reported in its daily intelligence update that “Ukrainian troops face significant resupply problems but have made an orderly withdrawal from the positions which they were forced to give up.”

Wagner is leading the Russians in this months-long battle that has been the deadliest for both sides. However, the leader of the mercenary groups had complained about the lack of support from the regular army for his troops.

The British update stated that “the Ukrainian defence still held the western districts in the town, but was subjected particularly intense Russian artillery firing over the past 48 hours.”

The report said that Wagner units are now concentrating on advancing into the Bakhmut centre, while Russian paratroopers relieve them to attack the city’s sides.

Bakhmut was the main target of Russia’s massive winter offensive, despite infantry combat on the ground that is unprecedented in Europe since World War Two.

The capture of the city would mark Russia’s biggest victory in eight month. Moscow has said it will open up a route for capturing more territory, which is a key war goal.

Ukraine is preparing its own counteroffensive. It had looked like it was going to abandon Bakhmut by the end of February but in March announced that it would continue to fight there because Russia was taking more casualties when it tried to storm it.