ITV News reporter Ben Chapman reports the latest from Ukraine
They say their troops have cut off vital supplies from reaching the Russian frontline. The reports follow several days of apparent advances by Ukraine south of the second largest city of Kharkiv.
Ukrainian Foreign Ministry spokesman Oleh Nikolenko suggested that troops had retaken Kupiansk, a town along the main supply route to Izyum, long a focus on the Russian front line and the site of heavy artillery and other fighting.
The Security Service of Ukraine later posted a message which it said showed its forces in Kupiansk, further suggesting it had been seized by Ukrainian troops.
The Ukrainian military didn't immediately confirm entering the town, a railway hub which Russia seized in February, when its mayor surrendered to avoid civilian casualties.
The Ukrainian Defence Forces also claimed they had captured much of the town of Balakliya, posting a video of the Ukrainian flag flying in the town centre.
Later today more videos on social media began to circulate, appearing to show Ukrainian forces on the rural outskirts of Izyum at a roadside checkpoint.
In its daily update, the UK's Ministry of Defence said that over the past four days Ukrainian forces had advanced up to 50km into previously Russian occupied territory.
They added that Russian forces were "likely taken by surprise."
Most recently, Russia's defence ministry announced troops would be pulled back from key areas in the Kharkiv region.
The Ukrainian military claimed in its regular update today to have taken “more than 1,000 square kilometers” from pro-Kremlin forces this week. It said “in some areas, units of the Defense Forces have penetrated the enemy’s defenses to a depth of 50 kilometers."
On Friday, Ukrainian President Volodymyr Zelenskyy said in his nightly video address that Ukrainian troops had reclaimed more than 30 settlements in the Kharkiv region since the start of the counteroffensive.
“We are gradually taking control over more settlements, returning the Ukrainian flag and protection for our people,” he said.