MEXICO CITY, Dec 2 (Reuters) - Billionaire Carlos Slim's America Movil said on Wednesday that trading in the shares of the spinoff of its Mexican wireless transmission towers will begin on Dec. 21, after receiving authorization from regulators.

Mexico's National Banking and Securities Commission authorized the listing of Telesites shares on Wednesday, America Movil said in a statement.

Telesites shares will form part of Mexico's benchmark IPC stock index, the company said.

America Movil, Latin America's biggest wireless and pay-TV provider, was knocked off its perch this week as the top-weighted company in the IPC index following a slump in its share price.

The company reported its first quarterly loss in 14 years in October due to sharp losses in Latin American currencies and a squeeze on its profit margins by tougher regulation in Mexico, its biggest market.

(Reporting by Michael O'Boyle; Editing by Leslie Adler)