With virtually no independent reporting from the front lines and Kyiv saying little, it was impossible to assess whether Ukraine was penetrating Russian defences in its bid to drive out occupying forces.
“We can state for sure that this offensive has begun,” Russian President Vladimir Putin said in Sochi.
“Ukrainian troops did not achieve their goals in any sector.”
Ukraine’s President Volodymyr Zelenskiy said he had discussed tactics and “achievements” with military leaders but gave little away.
“For our soldiers, for all those who at this time are engaged in particularly heavy combat – we see your heroism, and we are grateful for every moment of your lives,” he said in his nightly video address.
“Ukraine is as free as you are strong.”
Ukrainian military analyst Oleksander Musiyenko, interviewed on Ukrainian NV Radio, said Ukraine was making gains but dismissed Russian reports of a major counteroffensive in the south-central Zaporizhzhia region.
“This is simply not true,” Musiyenko said.
“It is not the main phase of the counteroffensive.
“It is merely a phase and not the large drive from which we can expect a rapid breakthrough and hundreds of kilometres of liberated territory.”
The counteroffensive is ultimately expected to involve thousands of Ukrainian troops trained and equipped by the West.
The US announced an extra $US2.1 billion ($A3.1 billion) in security assistance on Friday, including air defence and ammunition.
Russia, which has had months to prepare its defensive lines for the counteroffensvie, says it has repelled attacks since the start of the week.
Kyiv has said its main effort has yet to begin.
The southern front is where Ukrainian forces are widely expected to attempt their main push, towards the coast.
Deputy Defence Minister Hanna Maliar said battles were continuing for Velyka Novosilka and Russian troops were mounting “active defence” at Orikhiv.
In the east, Ukraine has reported advances around Bakhmut, which Russian forces captured last month after almost a year of the deadliest ground combat in Europe since World War II.
Ukraine generally bars journalists from reaching its side of the front lines during offensive operations.
Reuters could not independently verify the accounts by either side.
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 of people have been forced to evacuate homes flooded in the war zone, vast nature preserves have been wiped out and the destruction of 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 but argue Ukraine would have no reason to inflict such a devastating disaster on itself, especially right as its forces were shifting onto the attack.
In Hola Prystan on the Russian-occupied side of the river, rescuers evacuated residents in rubber dinghies.
Villagers carried pets or small children to safety.
Some relatives of people in Russian-controlled flooded areas said their loved ones were still stuck on roofs with dwindling food supplies.
The United Nations has no access to those areas, its humanitarian co-ordinator in Ukraine Denise Brown said, adding some 17,000 people were affected in Ukrainian-controlled areas, with numbers changing “by the minute”.
The river divides the two sides, which accuse each other of shelling across it, interfering with rescue efforts.