The 24-year old Malian striker has signed a four-year deal with the Hammers and is excited about continuing his career with the Premier League club.
"I am really happy and excited about joining West Ham United. I know West Ham are a big club in England and I'm really looking forward to representing them," he said.
"They have huge tradition and it is like joining part of a family and that is one of the main reasons I wanted to come here.
"I know some of the big names that have played for the club in the past and I am proud to be part of a new team back in the Premier League."