The Russian army is "throwing all its reserves into" capturing the city of Severodonetsk in the eastern Luhansk region, according to Serhiy Hayday, the head of the regional military administration.
"They had previously managed to capture most of the city, but now our military has pushed them back," Hayday told Ukrainian television, claiming the Russians are "suffering huge losses."
Hayday also said Chechen forces who appear to have thought the battle was won had entered the city.
He said the Russians were trying to demolish bridges "so that we cannot provide reinforcements to our guys who are in Severodonetsk, who are defending the Luhansk region. ... They are really afraid that the success of our defenders will develop, and this can be done if ammunition, weapons and reinforcements are provided in time. This is the first thing they are afraid of."
Earlier Saturday, Hayday said Ukraine now controls about half of Severodonetsk. He was responding to a question about the latest UK intelligence assessment, which had predicted Russia would control all of the Luhansk region within two weeks.
The humanitarian situation is difficult in the area, he added.
"At present, we can neither evacuate people nor bring humanitarian aid, for example, to Severodonetsk. The only places where we can deliver humanitarian cargo — food, medicine — are Lysychansk and the Hirske community," which are to the south of Severodonetsk, he said.
"Even in Lysychansk, we are shelled, but daily we continue to transport humanitarian goods by trucks. We may even evacuate people, but quietly, without publicity, because the Russian army is shooting at evacuation buses," Hayday claimed.
Oleksandr Striuk, head of the Severodonetsk military administration, said late Saturday that street battles continue in the city, and "our military is doing everything to drive the enemy out of the city."
Striuk said that residential areas of the city are now "divided in half."
"Street battles are being fought, which is accompanied by constant artillery shelling. The situation is quite tense, but there is hope and confidence in our armed forces that everything will work out. The city remains Ukrainian,” he said.
He said there had been about 13,000 people in the city before it was stormed by Russian troops, but some had been "forcibly removed to the occupied territory."