MEXICO CITY (Reuters) - Billionaire businessman Carlos Slim has increased his indirect stake in America Movil (>> America Movil SAB de CV) to about 15.8 percent since August, according to filings with the U.S. Securities and Exchange Commission.

The filings show that Slim's real estate company, Inmuebles Carso (>> Inmuebles Carso SAB de CV), and his bank, Grupo Financiero Inbursa (>> Grupo Financiero Inbursa SAB de CV), bought $248 million and $9.5 million, respectively, in America Movil stock since early August.

Slim's indirect stake in America Movil, including shares held through these companies, effectively increased from 15.2 percent since the last filing in July. His direct holding of America Movil shares did not change.

Shares of America Movil, which reported a sharp drop in quarterly results on Thursday, have fallen almost 9 percent this year. The company has spent more than $4.5 billion to date buying back shares.

The filing on Friday showed that Slim's other companies have been supporting that buyback effort.

The Slim family holds the majority of America Movil's voting shares.

America Movil shares closed at 13.660 pesos on Friday.

(Reporting by Elinor Comlay; Editing by Leslie Adler)