A Ukrainian advance near the eastern city of Kharkiv – which has recaptured several towns – has taken Russia “by surprise”, UK defence officials say.
In a daily update, they said Kyiv’s forces have advanced 50km (31 miles) into previously Russian-held territory.
The attack has also left thousands of Moscow’s troops “increasingly isolated” near the key city of Izyum, they said.
On Friday evening, President Volodymyr Zelensky said Ukraine had retaken 30 settlements in the Kharkiv region.
Speaking from Kyiv during his nightly address, Mr Zelensky said his forces are “gradually taking control of new settlements” and “returning the Ukrainian flag and protection for all our people”.
Ukraine launched its counter-offensive in the east earlier this week, while international attention had been focussed on an anticipated advance near the southern city of Kherson.
Analysts believe Russia had redirected some of its most seasoned troops to defend the city.
In their update, UK officials said “Russian forces were likely taken by surprise” by the eastern offensive.
The Kharkiv region was “lightly held”, the UK said, adding the offensive is seeking to sever Russian supply lines near Kupyansk and trap thousands of Russian troops in Izyum.
“We are moving forward,” General Valeriy Zaluzhnyi, commander of Ukraine’s armed forces, wrote in a Facebook update on Friday afternoon. “We clearly know what we are fighting for and we will definitely win.”
On Friday a Russia-appointed official in the Kharkiv region admitted that Ukrainian forces had won a “significant victory”.
“The very fact of a breach of our defences is already a substantial victory for the Ukrainian armed forces,” Vitaly Ganchev told state TV.
The Kremlin has so far refused to comment on the pace of the offensive, but Russia’s defence ministry published a video allegedly showing the transfer of troops towards Kharkiv.
And footage on social media appeared to show Russian forces being flown in to defend Izyum after the nearby settlement of Balakliya fell to Ukraine.
Speaking in Brussels on Friday, US Secretary of State Antony Blinken said the attack was “demonstrably making real progress”.
“I think we can say that Ukraine is proceeding in a very deliberate way with a strong plan and critically enabled by the resources that many of us are providing,” Mr Blinken said.
Mr Zelensky also said during his address that national police units were returning to liberated settlements and urged civilians to report suspected Russian war crimes to them.
His call followed a report from the UN’s monitoring team in Ukraine which said they had “documented a range of violations against prisoners of war” by Moscow’s forces.
The report also accused Ukrainian troops of “cases of torture and ill-treatment of prisoners of war”.
Despite optimism in the east, Mr Zelensky observed in his address that “fierce battles” have continued in the Donbas.
And the Ukrainian advance in the south also appears to be moving slowly, where Russian forces have put up intense resistance.
Elsewhere, German Foreign Minister Annalena Baerbock arrived in Kyiv on Saturday in a surprise visit, which she said was to demonstrate Berlin’s commitment to Ukraine’s defence.
“I have travelled to Kyiv today to show that they can continue to rely on us,” Ms Baerbock said. “That we will continue to stand by Ukraine for as long as necessary with deliveries of weapons, and with humanitarian and financial support.”
And on Friday, Mr Zelensky awarded the Order of Merit, Ukraine’s highest honour, to Haluk Bayraktar – the head of Turkish drone manufacturer Bayraktar.
The company’s TB2 combat drone, which can carry four missiles, has become a symbol of Ukrainian resistance.
While Ankara has sought to play the role of intermediary between Kyiv and Moscow since the conflict broke out, Mr Bayraktar has refused to supply Russia with arms and told CNN in August “we support Ukraine, support its sovereignty, its resistance for its independence”.(BBC)
•PHOTO: A Ukrainian soldier in a retaken area