A substantial Ukrainian force was pushing an assault against Russian positions in the south on Thursday, in an intensification of fighting that some Ukrainian officials and western analysts said marked the start in earnest of Kyiv’s much-vaunted counteroffensive. The combat against Russian positions south of Zaporizhzhia included western-supplied tanks and armoured vehicles and infantry backed by artillery. There were reports of intense fighting outside of the town of Tokmak, a key Russian logistical hub. Asked about US media reports that the counteroffensive had begun, a spokesman for Ukraine’s general staff said: “We have no such information. And we do not comment on anonymous sources.” Ukrainian officials, however, have insisted that they would not make an official announcement when the counteroffensive begins and have cautioned against focusing on a single area, suggesting it could involve a number of components. The Institute for the Study of War, a US-based thinktank that has been producing daily updates on the war, said it had concluded on Thursday that the Ukrainian counteroffensive had begun. “Activity throughout Ukraine is consistent with a variety of indicators that Ukrainian counteroffensive operations are under way across the theater,” the group tweeted. Following days of heavy shelling of Russian defences, Ukrainian units were reported to have stepped up efforts to break thorough in the Orihiv-Tokmak sector, which blocks the route to the Russian-occupied city of Melitopol – a key objective for Kyiv. Unconfirmed reports suggested that German-made Leopard tanks and US Bradleys had been thrown into the battle along with scores of other armoured vehicles. The Russian defence minister, Sergei Shoigu, said Ukrainian forces from Ukraine’s 47th mechanised brigade, with up to 1,500 troops and 150 armoured vehicles, made “an attempt to break through” but Russian forces dealt the attack “a preventive blow”, although Russian military bloggers painted a far more nuanced picture. Images posted by the Russian military blogger Rybar purported to show Ukrainian armour immobilised during the assault although neither those claims nor those of Shoigu could be verified. Vladimir Rogov, a Russian occupation official in the area, also told the RIA Novosti news agency that Ukraine’s forces were exerting “maximum force” against Russian positions in the Zaporizhzhia region. Russia has long anticipated a Ukrainian offensive in this direction, building multi-tiered defences around this area of the frontline including zig-zag trenches, dragon’s teeth and other obstacles. Claims that Kyiv is escalating efforts in the Zaporizhzhia area followed days of heavy shelling, with fires visible on Nasa’s Firms satellite monitoring system. Appearing to confirm that a major assault was under way, the Ukrainian deputy defence minister, Hanna Maliar, said Russia was “actively on the defensive” in the Orihiv area of Zaporizhzhia region. Speaking to ABC news, two Ukrainian officials, including a source close to President Volodymyr Zelenskiy, seemed also to confirm an active phase of the Ukrainian counteroffensive. While firm details of the fighting remained shaky, Ukrainian efforts appeared to be concentrated on the village of Robotnye, the Orihiv-Tokmak highway and outside Orihiv itself. On Telegram, the Russian military blogger channel War Gonzo discounted early claims by some that the Ukrainian effort was becoming “bogged down” saying it remained “too early to say” and describing a “hard night” for Russian forces around Orihiv. “It is reported from the scene that in the direction of Orihiv-Tokmak the enemy infantry continues to approach and try to gain a foothold. Enemy artillery and tanks are still intensively working on our positions. “Our troops hold the line and do not allow a breakthrough of the front, destroying enemy manpower and equipment. According to information from the field, our fighters managed to knock out a tank similar to the Leopard, but it is still impossible to identify the destroyed equipment for certain.” Other Russian sources spoke of an assault with armour and infantry on Robotyne with both Ukrainian and Russian aviation active and strikes reported on Tokmak itself on Thursday. One account posted on Twitter, purportedly by a Ukrainian soldier, described troops struggling to clear pathways through minefields around Malaya Tokmak. The fighting near Zaporizhzhia will be intensely scrutinised as this area of the front has long been seen as a potential axis for a Ukrainian assault towards Melitopol, not least because Tokmak itself is a major railway junction and Russian logistical hub that has key lines of communication with Mauripol, Berdyansk and Crimea. Another objective of a Ukrainian assault south and east from this direction has long been supposed to sever the Russian “land bridge” linking areas of the occupied south and east with Crimea. On 3 June, Zelensiky announced that the armed forces of Ukraine were ready for the long-awaited counteroffensive. “I don’t know how long it will take,” he told the Wall Street Journal. “To be hon­est, it can go a vari­ety of ways, com­pletely dif­fer­ent. But we are go­ing to do it, and we are ready.” Commenting on whether the destruction of the Kakhovka dam earlier this week might hinder Kyiv’s efforts, US analyst Michael Kofman said: “If the Ukrainian plan is to break through [Russian] lines in Zaporizhzhia and advance to the ground lines of communication from Crimea, or sever the ‘land bridge’ the resultant flooding is unlikely to impede such an operation.” Ben Barry, senior fellow for land warfare at the International Institute for Strategic Studies, was among those suggesting the counteroffensive had now begun. “Since 4 June Ukrainian forces have been attacking along the front line. This seeks to pin Russian forces in place and probe for weaknesses. “Probably, at the moment, it is mainly conducted by brigades already in place. It’s not clear if any of the dozen Ukrainian brigades trained and equipped for the counteroffensive have yet been committed. “A signature indicator would be large numbers of western armoured fighting vehicles including: Leopard and Challenger 2 tanks, Bradley and Marder infantry fighting vehicles and M113 APCs. “Russian bloggers are now reporting Leopards and Bradleys attacking in Tokmak in Zaporizhzhia Oblast. If confirmed, it suggests at least one Ukrainian assault brigade has been committed. “Russia plans to fight linear defence battles from trench lines, exploiting obstacle belts, falling back on deeper defensive positions when pressed. “I’d comment that if Ukraine can rapidly break through a defensive belt or belts, it could get behind the Russian defences and unpick them.”