What is Ukraine's Azov Brigade, on which US lifted its arms ban?

US has permitted the delivery of weapons and training to Ukraine's 'Azov Brigade', which has been described by Russia as an "ultranationalist armed formation". The brigade, formed in 2014, has been incorporated into Ukraine's National Guard but was earlier deemed as an entity whose founders possessed neo-Nazi ideologies by the US. Human Rights Watch had earlier raised concerns about Azov.