The US-based Institute for the Study of War said Russian troops appeared to have been ordered to hold off from a full assault.

“Russian forces continue to receive personnel and equipment reinforcements as well as command and control and logistics capabilities even as they conduct air and artillery preparations and some mechanised advances,” it said. “Only the advance to and possibly through Kreminna made significant progress.”

Ukrainian forces said they were holding firm after losing the town of Kreminna on Tuesday. Outgunned, but with high morale bolstered by US satellite intelligence, they said they would fight for every village in Donbas.

Russia has signalled that victory there by the May 9 Victory Day parade in Moscow – an annual highlight for Putin – would qualify the war as a success.

After nearly two months of fighting both armies are tired and, coupled with muddy spring conditions, logistics will play a major role in securing a victory.

“Russian attacks on cities across Ukraine show their intent to try and disrupt the movement of Ukrainian reinforcements and weaponry to the east of the country,” the Ministry of Defence said.

Russian media also said another Russian commander, Mikhail Nagamov of a sapper regiment, had been killed in action. Russia’s army has lost dozens of senior commanders in the war.