MEXICO CITY, Sept 3 (Reuters) - America Movil on Thursday said it was canceling by mutual agreement a contract with Spain's Telefonica to buy its El Salvador unit, Telefonica Moviles El Salvador, blaming regulatory hurdles.

America Movil, controlled by the family of Mexican tycoon Carlos Slim, owns telecommunications firm Claro in El Salvador and had been aiming to acquire for $315 million Telefonica Moviles and another El Salvador unit, Telefonica Multiservicios.

The two Telefonica units operate in the Central American nation under the Movistar brand and belong to Telefonica Centroamerica Inversiones.

El Salvador's Competition Superintendent regulator last month said it would allow America Movil to expand its market share on guarantees that it will abide by competition and consumer protection safeguards. It also limited the future use of Movistar's mobile phone spectrum.

America Movil said it was abandoning plans to buy 99.3% of Telefonica Moviles by mutual agreement with the Spanish telecoms giant.

"The decision is made after jointly assessing the conditions imposed to achieve regulatory authorization required in the final resolution recently issued by the Competition Superintendent," America Movil said in a statement.

The statement did not mention Telefonica Multiservicios or whether if that deal was off as well.

(Reporting by Diego Ore; Writing by Drazen Jorgic; Editing by Sandra Maler and Dan Grebler)