The 25-year-old, a Guinea international, has joined Rangers on a three-year deal and becomes boss Jimmy Floyd Hasselbaink's sixth summer signing.
Burnley are set to beat Hull City to the signing of Derby County midfielder Jeff Hendrick, sources close to the club have told ESPN FC.
The defender, who turns 20 on Friday, recently signed a new four-year contract with the Hammers.
The 22-year-old has signed a four-year contract after moving from South Yorkshire for an undisclosed fee.
Jonathan Kodjia has joined Aston Villa from Bristol City in an £11 million deal which could rise to £15m.
Hull City have signed goalkeeper David Marshall from Cardiff City for an undisclosed fee.