According to the latest update from the Ministry of Defence (MoD) stiff resistance had made Russia resort to significant use of auxiliary personnel.
Britain’s Ministry of Defence said in its daily intelligence report on Wednesday that Ukraine had bitterly contested the strategic port city, costing Russia time and troops as it sought to capture a land corridor from its home territory to the Crimean Peninsula, which it seized from Ukraine in 2014.
Mariupol was targeted by Russia in the early days of the invasion.
The MoD update reads: “Despite Russian forces having encircled Mariupol for over ten weeks, staunch Ukrainian resistance delayed Russia’s ability to gain full control over the city.
"This frustrated its early attempts to capture a key city and inflicted costly personnel losses amongst Russian forces.
"In attempting to overcome Ukrainian resistance, Russia has made significant use of auxiliary personnel. This includes a deployment of Chechen forces, likely consisting of several thousand fighters primarily concentrated in the Mariupol and Luhansk sectors."
It continued: “These forces likely consist of both individual volunteers and National Guard units, which are routinely dedicated to securing the rule of Chechen Republic Head, Ramazan Kadyrov.
"Kadyrov likely maintains close personal oversight of the deployment, while his cousin Adam Delimkhanov has likely acted as the Chechen field commander in Mariupol.
"The combat deployment of such disparate personnel demonstrates Russia's significant resourcing problems in Ukraine and is likely contributing to a disunited command which continues to hamper Russia’s operations.”
The Russian parliament plans to take up a resolution today to prevent the exchange of Azov Regiment fighters, who held out for months inside the Azovstal steelworks plant while Mariupol was under siege, according to Russian news agencies.
Ukraine’s deputy defence minister, Hanna Maliar, said negotiations for the fighters’ release were ongoing, as were plans to rescue fighters who are still inside the sprawling steel plant.
Ukrainian President Volodymyr Zelensky said “the most influential international mediators are involved” in the plans. Officials have not said how many remain inside.
The troops in the waterside steel plant have been the last pocket of resistance in Mariupol, which has been effectively in Russian hands for some time now.