Most of the Ukrainian city of Sieverodonetsk has been seized by Russian forces, UK and Ukrainian sources said on Wednesday.
Russian Foreign Minister Sergei Lavrov said the supply of US advanced rocket launchers to Ukraine raised the risks of a "third country" being dragged into the conflict.
Lavrov was responding to a question at a news conference in Saudi Arabia about US plans to provide Ukraine with advanced rocket systems that can strike with precision at long-range Russian targets.
Sievierodonetsk
Luhansk regional governor Serhiy Gaidai said Russian forces are now in control of around 70% of the strategically important city in Ukraine's Luhansk region.
"Over half of the town is likely now occupied by Russian forces, including Chechen fighters," the UK Defense Ministry said in a Wednesday morning intelligence update.
"Russian ground operations remain tightly focused, with the weight of fire power concentrated within a small sector of Luhansk Oblast," continued the ministry. "Over 30-31 May, fighting intensified in the streets of Sieverodonetsk, with Russian forces pushing closer to the town center.
"Some Ukrainian troops have retreated to more advantageous, pre-prepared positions," Gaidai said on the Telegram messaging app.
War casualties
In an interview with Newsmax, Ukrainian President Volodymyr Zelensky revealed that the situation was "very difficult" in terms of losses throughout the war.
"We're losing 60-100 soldiers per day as killed in action and something around 500 people as wounded in action,"he said.
As the war nears its 100th day, the Ukrainian military claims that Russia had lost 30,700 personnel since the invasion began.