Kyiv announced on Sunday that Ukrainian forces have retaken a village in the war-torn country's southeast, the first reported gain of the offensive.
After months of building expectations, Ukrainian President Volodymyr Zelensky said Saturday that a counteroffensive against Russian forces was underway but refused to provide any details.
Ukraine's ground forces said in a statement on Sunday that soldiers of the 68th separate ranger brigade had "liberated the settlement of Blagodatne" in the eastern region of Donetsk.
The ground forces released a video showing soldiers hoisting a Ukrainian flag over a destroyed building.
Another military spokesman, Valeriy Shershen, said in televised remarks that the retaken village was located on the border of the eastern region of Donetsk and the southern region of Zaporizhzhia where Moscow has reported heavy Ukrainian assaults over the past week.
He said Ukraine's forces captured several Russian and pro-Russian troops.
Big Ukrainian military successes in the Zaporizhzhia region could potentially enable its forces to break through the land bridge that connects Russia with the Crimean peninsula it annexed from Ukraine. This would be a major reversal for Moscow.
Ukraine has largely been silent on the offensive, but Russian President Vladimir Putin on Friday said Kyiv's fightback had already begun but was already failing.
Washington-based think tank the Institute for the Study of War said Saturday that Kyiv's forces conducted counteroffensive operations in at least four front-line areas.
- 'Worst since Chernobyl' -
Kyiv reported the first gain of the long-awaited offensive as thirty five people, including seven children, were still missing in southern Ukraine following a devastating flood prosecutors called the "worst environmental catastrophe since Chernobyl."
The Russian-controlled Kakhovka dam along the front line in the Kherson region was destroyed on Tuesday, forcing thousands to flee and sparking fears of humanitarian as well as environmental disasters.
Ukraine accuses Russia of blowing up the dam on the Dnipro River, while Moscow says Kyiv fired upon the structure.
Ukrainian Interior Minister Igor Klymenko said that 77 towns and villages had been flooded in the southern regions of Kherson and Mykolaiv.
Klymenko said that in the Kherson region 35 people were missing, including seven children.
As a result of the flood, five people died in the region of Kherson and one person was dead in the region of Mykolaiv, he said.
A total of 3,700 people have been evacuated from their homes in the two regions, the minister added.
In the city of Kherson, the largest population centre near the dam, the water began to subside and locals began to return to their homes to assess the damage, an AFP correspondent at the scene said.
Ukrainian rescuers in orange boats continued their efforts to evacuate people from the city's most affected areas and nearby islands.
An employee at Kherson's meteorological agency, Lora Musiyan, said the level of water dropped by 1.7 meters (5.5 feet) from the peak measurements recorded this week.
Oleksiy Gesin visited his grocery store in central Kherson for the first time in six days. Armed with a shovel and wearing rubber boots and a jacket, he cleared up debris in pouring rain. He said he sustained "significant" losses.
"The water in the store was up to my chest," he told AFP, adding that food will have to be thrown away.
- 'Very complicated' -
Ukrainian Prosecutor General Andriy Kostin and representatives of the International Criminal Court visited the region of Kherson, his office said.
"This is the worst environmental catastrophe since Chernobyl so we are investigating not only a war crime but also an ecocide," Kostin was quoted as saying in a statement.
"The situation is very complicated," he added.
He noted that a number of "dangerous" facilities including at least three cemeteries, oil storage terminals and garbage dumps have been flooded.
A total of 450 tonnes of turbine oil have spilled into the waters of the Dnipro and the Black Sea, he said.
More than 170 prosecutors have been investigating the breach of the dam.
"Our colleagues from the International Criminal Court are also with us," he said.
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