According to the UK defense ministry, it is "highly likely" that Ukrainian forces have reclaimed a piece of ground that Russia has held since 2014.
A Ukrainian commander reported Saturday that territory had been reclaimed close to the village of Krasnohorivka, which is occupied by Russia.
According to the UK's MoD, airborne forces have since made "small advances" east of that village in Donetsk.
The news comes as the leader of Ukraine claimed that his nation's counteroffensive was making progress on all fronts.
Volodymyr Zelensky said it was a "happy day" for Ukraine during his overnight speech, but he made no specific mention of any regions or provided any additional information.
The southern Crimean peninsula and more than a third of eastern Ukraine were illegally annexed by Russia in 2014.
According to the UK Defense Ministry's daily intelligence briefing, Ukraine's advances east of Krasnohorivka mark "one of the first times since Russia's February 2022 invasion that Ukrainian forces have highly likely recaptured an area of territory occupied by Russia since 2014.".
The defence ministry continues, "recent multiple concurrent Ukrainian assaults" across the Donbas - part of its counter-offensive efforts - are likely to have "overstretched Donetsk People's Republic and Chechen forces operating in this area.".
The evaluation has not been backed up by the BBC.
Earlier this month, Mr. Zelensky declared that the long-awaited counteroffensive by Ukraine to retake territory held by Russia had started. He acknowledged that battlefield progress has been "slower than desired" last week.
Ukrainian forces are "moving forward" in the south, according to Oleksandr Tarnavskyi, commander of the country's forces on the front lines in the south, who made the statement on Monday.
He said, without elaborating on which particular regions he was referring to, "There are already liberated territories and our movement continues.".
Mr. Tarnavskyi stated earlier on Saturday that troops had "liberated the territories near Krasnohorivka in the Donetsk region.".
Despite omitting any mention of Krasnohorivka specifically, the Russian defense ministry has insisted that its forces have "successfully repelled" attacks in disputed areas of the self-declared Donetsk People's Republic.
Pro-Russian war bloggers claim that Ukrainian forces have also made progress in the Kherson region and are moving to try to seize control of the left bank of the Dnipro.
Blogger for the military Sasha Kots wrote on Telegram that "in the past week, enemy activity on the Dnipro in the area of Antonovsky Bridge has grown abnormally.".
Russian occupying forces have had control over the left side of the Dnipro, while Ukrainian forces have had control over the right side. The Antonovsky Bridge did connect the two sides, though it sustained significant damage throughout the fighting.
Currently "entrenched," according to Mr. Kots, Ukrainian forces are "trying to expand the foothold" southward toward Crimea.
The BBC has not independently confirmed this, and Ukraine has not publicly announced its activities there.
