Russian Defence Minister Sergei Shoigu has said his troops have seized the key town of Mariinka in eastern Ukraine – a claim immediately denied by Kyiv.
Mr Shoigu told President Vladimir Putin assault units had taken the “powerfully fortified” area just outside Donetsk, a Russian-held regional capital.
But Ukrainian military spokesman Oleksandr Shtupun said “fighting for Mariinka” continued.
Mariinka – seen as a gateway to Donetsk – has been almost completely destroyed.
In a separate development, the Russian-installed head of Crimea, Ukraine’s southern peninsula seized by Moscow in 2014, reported an “enemy attack” and a fire in the port of Feodosiya in the early hours of Tuesday.
The head of the Ukrainian Air Force said his warplanes had destroyed a landing warship, the Novocherkassk, in the city.
Footage has emerged on social media purportedly showing a huge explosion in the port area.
The claims by both Russia and Ukraine have not been independently verified.
At a televised meeting with President Putin on Monday, Mr Shoigu said: “The assault detachments of the South group today completely liberated the settlement of Mariinka, which is five kilometres [three miles] south-west of Donetsk.
“For nine years, the armed forces of Ukraine have made a powerful fortified area, which is connected by underground passages. Each street has its own well-fortified and fairly well-protected structures from all attacks, both from the air and artillery, long-term firing points, complex underground communication systems.
“Thanks to the decisive actions of our servicemen, the fortified area has been cracked.”
Mr Putin hailed the reported capture as “success”, saying that Ukrainian troops had now been pushed further away from Donetsk, which they have been regularly shelling from Mariinka.
The Kremlin leader also said Russian forces now had the “opportunity to move into a wider operational area” in the Donetsk region.
Later on Monday, the Ukrainian military denied the Russian claim.
It was “incorrect to say that Mariinka is fully seized”, Mr Shtupun told Ukrainian TV.
“Our soldiers are currently within the administrative borders of Mariinka,” the military spokesman added.
Ukrainian military bloggers earlier reported that Ukrainian troops were holding out in a small area of western Mariinka.
The town has been used by Ukraine as a defensive barrier since 2014, when Russia-backed fighters seized large swathes of the eastern Donetsk and Luhansk regions.
President Putin launched a full-scale invasion of Ukraine in February 2022.
In recent weeks, Russian forces intensified their attacks in several key areas of a more than 1,200km-long (745 miles) battlefront.
Alongside Mariinka, they have been trying to encircle Avdiivka – another key town near Donetsk.
Ukrainian forces are seeking to extend their bridgehead on the left (eastern) bank of the Dnipro river in southern Ukraine.
Last week, Ukrainian President Volodymyr Zelensky said the country’s military were planning to mobilise up to 500,000 extra people.
His comments come as Ukraine is facing an ammunition shortage amid aid setbacks from its key allies in the US and the EU.
Kyiv’s counter-offensive ground to a halt at the start of winter and there are fears that the Russians could simply outgun Ukraine.