Ukrainian forces seized nearly a mile of land in 24 hours near the eastern town of Bakhmut by exploiting blunders by new Russian troops, military sources said on Friday.
Fierce fighting is taking place around the town in the Donetsk province of the eastern Donbas region.
Serhiy Cherevaty, spokesperson for Ukraine’s East military command said Ukrainian forces had advanced 1.2 km (0.75 mile) near Bakhmut over the past 24 hours.
“We took advantage of the enemy’s rotation measures and the fact that units which entered do not know the area fully, and failed to conduct appropriate reconnaissance and coordination. We struck,” he told Ukrainian television.
“We have been carrying out assaults for several days.”
Over the past several days, Ukrainian forces have made their most rapid gains around the edges of Bakhmut, aiming to encircle the ruined town which Russian forces seized control of last month.
“The situation is tense on all areas of the front,” Deputy Defence Minister Hanna Maliar said on the Telegram messaging app.
Naming eastern areas where fighting has been fierce for months, she said: “The enemy continues to focus its main efforts on the Lyman, Bakhmut, Avdiivsky and Mariinka directions, heavy fighting continues.”
She said Ukrainian troops were repelling the Russian attacks, though this could not be independently confirmed.
Meanwhile, Russia’s Defence Ministry said it was continuing to repel Ukrainian attacks in the southern region of Zaporizhzhia, Russian news agencies reported, though these claims could also not be firmed up independently.
Ukrainian officials made little mention of the situation in Zaporizhzhia but the head of the president’s office said a junior nurse and a plumber had been killed by Russian shelling of a hospital in Huliai Pole in the province.
The Institute for the Study of War stressed that Kyiv troops had made advances around the eastern town of Bakhmut.
But it also emphasised that Russian forces had apparently defended against an attack in the western Zaporizhzhia province “in a doctrinally sound manner”.
Ukrainian president Volodymyr Zelensky on Thursday hailed what he described as “results” in Donetsk region in eastern Ukraine.
“There is very heavy fighting in Donetsk region,” Mr Zelensky said in his daily video message.
“But there are results and I am grateful to those who achieved these results. Well done in Bakhmut. Step by step,” he said.
In further detail from the Washington-based think tank it said:
Ukrainian officials had signalled that Ukrainian forces have transitioned from defensive to offensive operations in the Bakhmut sector and are making gains of between 200 metres and nearly two kilometre (1.2 miles) on the flanks of the eastern town.
Ukrainian forces made tactical gains during limited localised counter-attacks in western Donetsk province, near the border with the Zaporizhzhia province.
Ukrainian forces also conducted an attack in western Zaporizhzhia province on the night of June 7 to 8 but do not appear to have made gains as part of this attack, or at least not early on, with Moscow claiming Russian troops had regained lost positions.
The ISW has warned that Ukrainian forces may face their hardest challenges as they seek to initially breach Russian defensive lines and so could suffer heavy losses in the early part of the counter-offensive.
Russia's army on Friday reported heavy fighting in the Donetsk and Zaporizhzhia regions of Ukraine, saying over 21 Ukrainian tanks had been destroyed in battles across key sections of the front line.
However, claims from Moscow need to be treated with caution given the often inaccurate propaganda issued by the Kremlin and Russian defence minsistry.
A spokesman for Russia's Vostok group of forces said 13 Ukrainian tanks were destroyed in battles in the Zaporizhzhia region and eight in the Donetsk region. It reported artillery, drone and infantry battles.
These claims could not be independently verified.
Russian military bloggers said there were intense battles on the Zaporizhzhia front near the city of Orikhiv as Ukraine sought to pierce Russian defences and drive a wedge through Russian forces.
Russia said Ukraine began a major offensive on Sunday morning, first in southern Donetsk, but Moscow said its forces repelled the attacks. Ukraine accuses Russia of spreading misinformation.
Meanwhile, Ukraine’s air force said on Friday that it shot down four cruise missiles and 10 attack drones during a Russian air strike overnight.
It said Russian forces had launched 16 drones and six cruise missiles during the attack, and that two other cruise missiles had struck a civilian object in central Ukraine during an earlier attack on Thursday evening.