With virtually no independent reporting from the front lines and Kyiv maintaining strict silence on its plans, it was impossible to assess whether Ukraine was having success in penetrating Russian defences to drive out occupying forces.
The counteroffensive is ultimately expected to involve thousands of Ukrainian troops trained and equipped by the West.
Russia, which has had months to prepare its defensive lines, says it has withstood attacks since the start of the week.
Kyiv has so far said its main effort has yet to begin.
Pro-war Russian bloggers reported intense battles on Friday on the Zaporizhzhia front near the city of Orikhiv, around the mid-point of the “land bridge” linking Russia to the Crimea peninsula, seen as one of Ukraine’s main potential targets.
Ben Barry, senior fellow for land warfare at the International Institute for Strategic Studies, said reports from the Russian bloggers of German-made Leopard tanks and US Bradley armoured vehicles near Tokmak south of Orikhiv, if confirmed, would provide the first evidence that Ukraine’s new brigades of Western-armed troops had joined the battle.
In all, Kyiv has 12 brigades totalling 50,000-60,000 troops ready to unleash in the counteroffensive. Nine of the brigades have been armed and trained by the West.
“They’ve got a choice of how many they commit initially and how many they keep in reserve in case the battlefield dynamics change,” Barry said.
The initial days of the counteroffensive have been overshadowed this week by a huge humanitarian disaster after the destruction of the Kakhovka dam holding back the waters of the Dnipro River that bisects Ukraine.
Thousands were forced to evacuate homes flooded in the war zone, vast nature preserves have been wiped out and the destruction to irrigation systems is likely to cripple agriculture across much of southern Ukraine for decades. Kyiv said at least four people had died and 13 were missing.
Ukraine’s security service released a recording on Friday of what it described as an intercepted phone call in which a Russian soldier confides to another man that a Russian sabotage group had blown the dam up. Moscow says Ukraine sabotaged it.
Western countries say they are still gathering evidence about who is to blame, but believe Ukraine would have no reason to inflict such a devastating disaster on itself.
The river serves as the front line dividing the two sides. Both accuse the other of shelling across it, interfering with rescue efforts. The Kremlin said Ukrainian shelling had killed people including a pregnant woman. It provided no evidence.
In Russia’s latest report from the battlefield, the army claimed to have destroyed 21 Ukrainian armoured vehicles in the past 24 hours. Such claims are unverifiable.
In Kyiv’s few comments on the fighting, it has reported gains of territory in the east around the city of Bakhmut, which Russian forces captured last month after nearly a year of deadly ground combat.
In his nightly video address, President Volodymyr Zelenskiy thanked Ukrainian troops and repeated earlier claims of success in Bakhmut, but gave no further account.
During the latest Russian air strikes, Ukraine said it shot down four of six missiles overnight.
The interior ministry said one person had been killed, three were wounded, and four buildings were destroyed by falling debris.
The air force also said two cruise missiles had struck a civilian object in the central Ukrainian region of Cherkasy earlier on Thursday evening. Regional governor Ihor Taburets said at least eight people were wounded.
Moscow said Ukraine had struck the Russian city of Voronezh with a drone, wounding three people. Kyiv withholds comment on reports of attacks inside Russia.