Ukraine sent Western tanks into battle for the first time in a major offensive on the southern front that marked the launch of its long-awaited counter-offensive.
Leopard II main battle tanks were seen in the Zaporizhzhia region, where a sudden surge in fighting appeared to mark the start of the assault.
Ukraine’s ministry of defence, which has a strict policy of operational silence around the offensive, denied reports that it had begun.
But Ukrainian officials speaking on condition of anonymity said an active phase of the counter-offensive was under way, US media reported.
US officials said that the latest assault appeared to be the main thrust of the counter-offensive.
However, officials cautioned that the Russians had put up “stiff resistance” and that the Ukrainians had suffered losses.
Speaking at a White House press conference with Rishi Sunak, Joe Biden, the US president, said he was “very optimistic” about the “evolving” situation.
Mr Sunak said it was “totally reasonable” for the American people to ask allies to “do their part”, adding that the UK was “proud” to be the biggest contributor behind the US to the military effort.
He said: “I think it is important other nations step up and do their part. President Putin will be thinking that the alliance will tire, will get fatigued, and that is not the case.”
Russia published a video of a long column of Ukrainian vehicles under heavy attack, as Vladimir Putin, the Russian president, was personally briefed on the “heavy losses” inflicted on Ukraine.
It came as Russia shelled the Ukrainian city of Kherson, targeting civilians evacuating the floodwaters after a major dam sent a torrent of water downstream.
Volodymyr Zelensky, the Ukrainian president, visited the city moments before the barrage rained down.
On Thursday Jens Stoltenberg, head of Nato, urged members of the alliance to speed up humanitarian assistance to Ukraine after the destruction of the dam.
The Ukrainian offensive appeared to be focussed around the Ukrainian-held front-line town of Orikhiv, with analysts suggesting Kyiv was intending to push down towards the coast and cut off Russia’s access to Crimea.
But Russia claimed to have largely repelled the attack. Ukrainian and Western officials have long warned that the counter-offensive would be difficult, even with fresh supplies of modern Nato-standard equipment like main battle tanks.
The Russians have prepared multi-layered defensive lines several miles deep in Zaporizhzhia, including minefields, trenches, and tank traps.
Earlier, Russian sources reported “wave after wave” of Ukrainian infantry and armour attacks in the south of the country for the fourth successive day.
Sergei Shoigu, the Russian minister of defence, told Putin that Moscow forces had defeated a large attack by Ukraine’s 47th mechanised brigade in a two-hour battle in the Zaporizhzhia region on Thursday morning. There was no way to verify the claim.
Russian drone pictures circulated by pro-Kremlin social media showed several vehicles, including two Leopard main battle tanks, at a junction outside Malaya Tokmachka.
The images showed some vehicles burning after apparently being hit by mines or artillery.
Military observers said at least one of the Leopards was among the vehicles damaged or destroyed.
Britain’s Ministry of Defence said in an intelligence update that “amidst a highly complex operational picture, heavy fighting continues along multiple sectors of the front. In most areas Ukraine holds the initiative”.
None of the claims about the progress of the battle could be independently verified, and were likely part of both sides’ propaganda campaigns.
However, independently geolocated images confirmed that a battle was under way and suggested Ukraine may have committed advanced Western weapons to the fight.
Russian bloggers, many of them with close ties to the military and a record of downplaying Ukrainian successes, claimed multiple attacks were repulsed near the Ukrainian-held frontline town of Orikhiv.
“Active operations began around 3am, the most intense fighting took place in the Novodanylivka area. The enemy managed to occupy the positions of the outrigger guard of the 291st motorised rifle regiment,” wrote one, citing contacts at the front.
Novodanylivka is a hamlet south-west of Orikhiv.
Another reported “wave after wave of the enemy is trying to break through our defence in the area of Malaya Tokmachka”, a village in the same area. It claimed the attacks were repulsed with heavy losses.
Volya, a Russian-language Telegram channel that claims to have contacts on both sides of the line, reported that Russia had suffered extremely heavy losses when it revealed concealed firing positions by prematurely engaging small Ukrainian probing forces.
Igor Girkin, a former Russian security services officer who has been a harsh critic of the Kremlin’s handling of the war so far, said Moscow forces appeared to have performed well so far on the defence, but warned Ukraine would attack in other areas.
Offensive operations on the southern front appeared to begin on Monday, with assaults around the village of Velyko Novosylka, 50 miles east of Orikhiv.
Ukraine has also continued to push forwards around Bakhmut, in Donbas, and to back cross-border raids by anti-Kremlin Russian militias further north, in a bid to stretch Kremlin defences.
The objective of the Ukrainian push around Orikhiv appears to be Tokmak, a village about 20 miles to the south that serves as the anchor of Russian defences in the central Zaporizhzia region.
The battle around VeVeliko Novosilka, which is believed to be continuing, threatens a similar line of advance on the border to the Zaporizhzia and Donetsk regions.
Attacks have also been reported around Kamenskoye, at the western end of the line.
It is not yet clear which attack will be the main thrust. Breaking the Russian lines in Zaporizhzhia region could allow Ukraine to threaten the “land bridge” connecting Russia to occupied Crimea.
Ukraine’s third separate assault brigade on Thursday said it had advanced a further 1.2km around Bakhmut.
It said about 30 Russian soldiers were killed and 40 wounded in an assault that pushed them behind a canal that the enemy had recently held.
Large explosions were reported in an industrial area of the Russian occupied city of Luhansk. Russian sources attributed them to UK-supplied Storm Shadow cruise missiles.
A senior Ukrainian defence official declined to confirm that the offensive had begun and suggested the Russian reports were exaggerated.
“When it starts you won’t have to ask for confirmation,” the official told The Telegraph
Mr Biden said: “The Ukrainians can speak to the military operations, I won’t do that from here. We’ve done everything we could collectively, individually, the United States, to support and be ready. In an evolving situation we’re very optimistic.”
Asked about moves by Republicans in Congress to limit funding to Ukraine, he said: “I believe we’ll have the funding to support Ukraine as long as it takes.
“I believe that support will be there even though you hear some voices on Capitol Hill about whether we should support Ukraine, and how long we should support it.”
Mr Biden added: “Do we think Russia would stop at Kyiv? I think not, and I think the vast majority of my colleagues, even the critics, think the same.”
He pledged “our unwavering support for the people of Ukraine” who he said were “defending themselves against the most brutal aggression we’ve seen in a long time at the hands of Vladimir Putin”.
He told Mr Sunak: “I want to thank you for your strong, strong support.”
The Prime Minister said more long-term support must be put in place for Ukraine.
He said: “Then it sends a strong signal to him [Putin] we’re not going anywhere, we will be there for as long as it takes. And hopefully that will speed up the calculation in his mind that he should withdraw his troops.”
Mr Biden was asked if it was time for a British secretary-general of Nato, a reference to Ben Wallace.
The president said: “It may be. That remains to be seen. We’re going to have to get a consensus within Nato to see that happen.
“They have a candidate who’s a very qualified individual, and we’re going to have a lot of discussion between us in Nato.”
