Ukraine said Tuesday its forces were under pressure in Bakhmut, a nearly-destroyed city in the eastern Donetsk region that Russia has been trying to seize for months.

"The situation around Bakhmut is extremely tense. Despite taking significant losses, the enemy has dispatched its best-trained Wagner assault units to try to break through the defences of our troops and surround the city," the commander of Ukraine's ground forces Oleksandr Syrskyi said on social media.

Moscow's troops, and in particular the paramilitary group Wagner, have been making slow progress toward capturing the city.

The industrial hub with a pre-war population of around 70,000 has become the epicentre of the grinding war in eastern Ukraine. 

This battle, the longest-running of Russia's year-long invasion, has involved mass artillery strikes, made high casualties on both sides, and reduced the city to rubble. 

Experts have downplayed the strategic importance of the city, but Bakhmut has turned into a key political and symbolic prize as the battle dragged on.

On Monday evening Ukrainian President Volodymyr Zelensky warned the situation around Bakhmut was getting increasingly difficult.