The UK Defense Ministry shared their regular report on Twitter.
"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," said the British intelligence.
In attempting to overcome Ukrainian resistance, Russia has made significant use of auxiliary personnel. This includes a deployment of Chechen forces, besides National GUard units, which are routinely dedicated to securing the rule of Chechen Republic Head, Ramazan Kadyrov. His cousin Adam Kadyrov has acted as the Chechen field commander in Mariupol.
This means that Russia’s significant resourcing contributes to a disunited command in Ukraine which continues to hamper Russia’s operations.