Kyiv (Ukraine) (AFP) – Ukraine's army on Saturday dismissed Russian claims to have seized the eastern stronghold of Kostyantynivka, saying the situation was "difficult" but that troops were defending the town.

President Volodymyr Zelensky called the Russian claim a "lie", a day after Russia's President Vladimir Putin appeared in military uniform on television thanking his forces for seizing the town.

"Ukrainian defenders continue to hold their positions along the designated defensive lines. The situation remains difficult but is under the control of the Ukrainian Defense Forces," army spokesman Andriy Kovalyov said.

He acknowledged that Russian troops have tried to seize the town and had infiltrated it in small groups.

"There have been instances of small infantry groups (1–3 personnel) infiltrating deep into the battle formations of Ukrainian forces. Counter-sabotage operations by the Defense Forces are ongoing in the town. Occupying forces are being detected and eliminated," Kovalyov said.

He said Russian carried out "11 assault attempts" on Friday -- when Moscow announced the seizure -- but said they "failed to achieve any success".

"The enemy has resorted to the dissemination of blatant disinformation and fake claims by its highest-ranking officials," he said.

Zelensky -- who said he briefed German Chancellor Friedrich Merz on the battle -- declared that Putin had "chosen to lie to the world" about the front.

"He claims that Russian forces have supposedly captured Kostyantynivka in the Donbas. Of course, that is not true. It is just another Russian lie," Zelensky said on social media.

"If Kostyantynivka were under Russian control, then perhaps Putin would have no problem meeting me there to find a diplomatic way to finally end this war," he added.

Putin has repeatedly turned down talks with Zelensky to end more than four years of war.

Russia has been trying to seize Kostyantynivka -- which had some 78,000 people before the 2022 invasion -- for months.