Ukraine’s military says it has broken through Russia’s first line of defence in the occupied Kherson region.
The reported push appears to form part of a long-awaited counter-offensive being launched by Kyiv in an attempt to retake the country’s south.
It follows weeks of Ukrainian attacks aimed at cutting off Russian forces there from main supply routes.
Russia’s military claims that Ukrainian troops suffered “heavy losses” during an unsuccessful attacking attempt.
The claims by both Ukraine and Russia have not been independently verified.
Kherson became the first major Ukrainian city to fall into Russian hands after troops advanced into the city from the Crimean Peninsula in the opening days of the war.
Early on Monday, Ukraine’s Kakhovka operational group in the south said that one regiment of Russian-backed forces had left its positions in the Kherson region. It added that Russian paratroopers providing the back-up had fled the battlefield.
Oleksiy Arestovych, adviser to President Volodymyr Zelensky’s head of office, later also said that Ukraine’s armed forces “have broken through the frontline in several places”.
Meanwhile, eyewitnesses reported hearing more blasts in the cities of Kherson and Nova Kakhovka, about 55km (34 miles) north-east from the regional capital. The key crossings across the Dnipro River in the two locations have been repeatedly targeted by Ukraine’s military in recent weeks.
Russia’s state-run Ria Novosti news agency reported that Nova Kakhovka was left without electricity and water supply overnight.
In his late night video address, President Zelensky issued a stark warning to Russian forces: “If they want to survive, it is time for Russian soldiers to flee. Go home.”
Mr Zelensky and other top Ukrainian officials have been tight-lipped about details of the reported counter-offensive, urging Ukrainians to be patient.
Responding to the Ukrainian claims, Russia’s defence ministry said that Ukrainian troops had attempted an offensive in the Kherson and neighbouring Mykolaiv regions.
The ministry is quoted by Russia’s state-run news agencies as saying this operation had failed, and that the Ukrainian troops had “suffered heavy losses”.
Kyiv officials claim to have used US-supplied Himars rocket systems to destroy three bridges crossing the Dnipro River. The military’s southern command also said it had destroyed makeshift Russian pontoon bridges over the river.
According to Western military sources, Kyiv’s strikes are part of a targeted effort to cut off Russian troops on the right (western) bank of the river with the ultimate goal of recapturing the entire Kherson region.
Moscow has relied on these bridges to resupply their troops.