Russia said Tuesday it was carrying out "massive strikes" across the Ukrainian front line and accused Ukrainian soldiers of abusing civilians in territories recaptured in a dramatic counter-offensive.
Moscow's retaliation came after it was forced to pull back its troops from swathes of the northeast, particularly in the Kharkiv region, following Kyiv's lightning assault to wrest back terrain.
The territorial shifts marked one of Russia's biggest setbacks since its troops were repelled from Kyiv in the earliest days of the nearly seven-month war, yet Moscow signalled it was no closer to agreeing to a negotiated peace.
"Air, rocket and artillery forces are carrying out massive strikes on units of the Ukrainian armed forces in all operational directions," the Russian defence ministry said in its daily briefing on the conflict.
"High-precision" strikes have also been launched on Ukrainian positions around Sloviansk and Konstantinovka in the eastern Donetsk region, it added.
The Kremlin accused Kyiv's army of abusing civilians in territory it had recaptured.
President Vladimir Putin's spokesman said that in the Kharkiv region, reports were emerging of "outrageous" treatment of civilians.
"There are a lot of punitive measures... people are being tortured, people are being mistreated and so on," Dmitry Peskov told journalists.
Russia's allegations came after Ukrainian authorities claimed to have found four bodies of civilians with "signs of torture" in the recaptured eastern village of Zaliznychne.
- 'Too early to tell' -
Residents reported that Russian troops had killed villagers, the regional prosecutor's office said, announcing a war crime probe.
Ukrainian forces launched their counter-offensive in early September, seemingly catching Russia's military off guard.
Images posted by the Ukrainian military showed crates of munitions and military hardware scattered across territory abandoned by Russian forces.
Around the north-eastern town of Balakliya, AFP journalists saw evidence of fierce battles, with buildings destroyed or damaged and streets mostly deserted.
By Monday, President Volodymyr Zelensky said that Ukraine's forces have retaken a total of 6,000 square kilometres (2,320 square miles) from Russian control.
In the northeast, dozens of areas including the cities of Izyum, Kupiansk and Balakliya, have been retaken, Ukraine said.
Ukraine has also claimed significant gains in the southern Kherson region, where the Ukrainian army also said it had recaptured 500 square kilometres.
US Secretary of State Antony Blinken assessed that the Ukrainians had made "significant progress", due to their resilience as well as US support.
"It's too early to tell exactly where this is going. The Russians maintain very significant forces in Ukraine as well as equipment and arms and munitions.
"They continue to use it indiscriminately against not just the Ukrainian armed forces but civilians and civilian infrastructure as we've seen," Blinken said on Monday.
- 'Turned the tide' -
A US think tank, the Institute for the Study of War, tweeted: "Ukraine has turned the tide in its favour, but the current counter-offensive will not end the war."
Defence Minister Oleksii Reznikov told French daily Le Monde in a Monday interview that the war has entered a new phase with the help of Western weapons.
Kyiv nonetheless ramped up its calls for Western allies to rush more sophisticated weapons to help in its fight.
"Weapons, weapons, weapons have been on our agenda since spring. I am grateful to partners who have answered our call: Ukraine's battlefield successes are our shared ones," Ukrainian Foreign Minister Dmytro Kuleba said.
But Germany was once again under the spotlight for failing to deliver Leopard battle tanks that Kyiv is seeking.
"Not a single rational argument on why these weapons cannot be supplied, only abstract fears and excuses," said Kuleba, after Chancellor Olaf Scholz dodged a question on the issue on Monday, saying only that Germany would not "go-it-alone" on weapons deliveries.
Away from the battlefield, Ukraine's allies were grappling with an energy crisis after Russia curtailed deliveries to the bloc.
Finnish Prime Minister Sanna Marin appealed for EU unity in the face of Russian "blackmail" over energy supplies, and for more sanctions on Moscow.
Seeking emergency measures to bring down soaring energy prices, the Czech Republic, which holds the rotating presidency of the EU, called an extraordinary meeting on September 30.