Ukraine's military said on Saturday it had killed scores of Russian soldiers and destroyed two ammunition dumps in fighting in the Kherson region, the focus of Kyiv's counter-offensive in the south and a link in Russian supply lines.
Rail traffic to Kherson over the Dnipro River was cut, the military's southern command claimed, potentially further isolating Russia's forces west of the river from supplies in occupied Crimea and the east.
Ukraine used western-supplied long-range missile systems to damage three bridges across the Dnipro in recent weeks, cutting off Kherson city and, according to an assessment by British defence officials, leaving Russia's 49th Army stationed on the west bank of the river vulnerable.
“As a result of fire establishing control over the main transport links in occupied territory, it has been established that traffic over the rail bridge crossing the Dnipro is not possible,” Ukraine's Southern Command said.
It said more than 100 Russian soldiers and seven tanks had been destroyed in fighting on Friday around Kherson, the first major town captured by the Russian forces following their February 24 invasion.
Yuri Sobolevsky, the first deputy head of the Kherson regional council, told residents to stay from away from Russian ammunition dumps.
“The Ukrainian army is pouring it on against the Russians and this is only the beginning,” Mr Sobolevsky wrote on the Telegram app.
Dmytro Butriy, the pro-Ukrainian governor of Kherson region, said Berislav district was particularly hard hit. Berislav is across the river north-west of the Kakhovka hydroelectric power plant.
“In some villages, not a single home has been left intact, all infrastructure has been destroyed, people are living in cellars,” Mr Butriy wrote on Telegram.
Officials from the Russian-appointed administration running the Kherson region this week rejected western and Ukrainian assessments of the situation.
Britain's Ministry of Defence said on Saturday that Russia was likely to have built two pontoon bridges and a ferry system to compensate for bridges damaged by Ukrainian strikes.
Russian-installed authorities in occupied territories in southern Ukraine were possibly preparing to hold referendums on joining Russia later this year, and were “likely coercing the population into disclosing personal details in order to compose voting registers,” the MoD claimed.
The two sides also traded accusations on Friday over a missile strike or explosion that appeared to have killed dozens of Ukrainian prisoners of war in eastern Donetsk province.
Forty prisoners were killed and 75 wounded at the prison in the frontline town of Olenivka held by Moscow-backed separatists, Russia's Ministry of Defence said.
A representative for the separatists put the death toll at 53 and accused Kyiv of hitting the prison with US-made Himars rockets.
Ukraine's armed forces denied responsibility, saying Russian artillery had hit the prison to hide the mistreatment of those held there.
President Volodymyr Zelenskyy said the shelling of a prison was a “deliberate Russian war crime”.
“Today, I received information about the attack by the occupiers on Olenivka (the prison's location), in the Donetsk region. It is a deliberate Russian war crime, a deliberate mass murder of Ukrainian prisoners of war. More than 50 dead,” he said in his daily address.
Reuters TV showed the remains of a cavernous burned-out building filled with metal beds, some with charred bodies lying on them while other bodies were lined up on military stretchers or on the ground outside.
Shell fragments had been laid out on a blue metal bench. It was not possible to detect any identifying markings and it was not clear where the fragments had been collected.
The International Committee of the Red Cross said it was seeking access to the site and had offered to help evacuate the wounded.
Ukraine has accused Russia of brutality against civilians since its invasion and said it has identified more than 10,000 possible war crimes. Russia denies attacking civilians.
Meanwhile, the US and Russian top diplomats discussed a United Nations-brokered deal to restart shipping grain from Ukraine and ease a worldwide food crisis in their first phone call since Russia attacked Ukraine in what it calls a “special military operation”.
Russia's Foreign Minister Sergey Lavrov told Secretary of State Antony Blinken that Washington was not living up to promises regarding the exemption of food from sanctions, the Foreign Ministry said.
A Russian account of the phone call quoted Mr Lavrov as telling Mr Blinken that Russia would achieve all the goals of its operation, and that western arms supplies to Ukraine would only drag out the conflict.
Mr Blinken warned Mr Lavrov about any Russian territorial claims during its war in Ukraine.
“The world will not recognise annexations. We will impose additional significant costs on Russia if it moves forward with its plans,” he said.