(Recasts with details on Slim's stake)
MEXICO CITY, June 27 (Reuters) - Carlos Slim's real estate firm, Inmobiliaria Carso, will buy AT&T Inc's equity stake in America Movil, tightening the Mexican tycoon's control of his flagship telecommunications firm, according to a filing with Mexico's stock exchange on Friday.
Slim's Inmobiliaria Carso will buy more than 5.7 billion "AA" shares that have been held by AT&T, equal to 8.27 percent of America Movil's stock, the Mexican telecommunications firm said in the filing.
The stake represents 23.81 percent of America Movil's voting stock. Inmobiliaria Carso and one of its subsidiaries will also buy 72.8 million shares of commonly traded "L" shares, according to the filing.
America Movil did not reveal how much Inmobiliaria Carso will pay for the shares. "AA" shares do not frequently trade, but if the whole deal were valued at the current price of "L" shares, it would be worth close to $6 billion.
Slim's firms and family already control more than 50 percent of America Movil's voting stock.
AT&T announced the plan to sell its stake in America Movil in May in order to help it gain regulatory approval for its purchase of DirecTV.
America Movil shares closed up 3.59 percent at 13.29 pesos per share. (Reporting by Tomas Sarmiento; Editing by Paul Simao)