Dr Jack Watling provides analysis on Russian tactics and supplies on Radio 4's Today programme

...What we're seeing now is a transition from where the Russians were resourcing multiple axes of advance into Ukraine and now they're having to concentrate that resource on one axis at a time essentially, so they're starting to dig a position around Kyiv, they're going firm around Kharkiv, and Mariupol is the main effort at the moment. Now if Mariupol falls then they can shift that main effort somewhere else..."