(Adds comment from analyst, closing stock price, details on AT&T's performance)
By Julia Love and Noe Torres
MEXICO CITY, Oct 24 (Reuters) - Mexican billionaire Carlos Slim's America Movil on Tuesday reported a net loss of 9.55 billion pesos ($525 million) for the third quarter, with its results dragged down by a costly Colombian arbitration panel ruling.
The flagship company of Slim's business empire registered a profit of 2.12 billion pesos in the same quarter a year earlier. Revenues of 244.2 billion pesos for the quarter were down from 249.7 billion pesos during the same period last year.
While the peso's depreciation took a toll, the company said the biggest factor in its loss was an 18.5 billion peso payment made as a result of the July ruling by the arbitration panel.
The Colombian panel said America Movil and Spain's Telefonica failed to return installed telecommunication networks and infrastructure as part of agreements to provide cellular phone service in Colombia more than a decade ago.
America Movil is challenging the ruling. Were it not for the payment, the company said it would have registered a net profit of 2.5 billion pesos.
Natural disasters in Mexico and Puerto Rico hurt revenues, America Movil said. Services revenues plunged 17.4 percent in the quarter in Puerto Rico, which was battered by Hurricane Maria in September, knocking out power and phone lines.
Analysts said the performance reflected America Movil's tough circumstances during the quarter, rather than underlying weakness in the business.
"The quarter was charged with non-recurring effects, namely the payment in Colombia, foreign exchange losses, a harder comparison base and the natural disasters in Mexico and Puerto Rico," said Gerardo Cevallos, an analyst with brokerage Vector.
America Movil touted progress in nudging its business toward mobile data, widely viewed as a key engine of growth. Revenue from mobile data climbed 24.3 percent from the previous year in Latin America, with an 8.5 percent increase in Mexico.
"In Latin America, mobile data revenues led the way," the company said in a statement accompanying its results.
Shares in America Movil have been on the rise since the Mexico Supreme Court ruled in August that the company should not be barred by law from charging its competitors certain fees.
Stemming from the 2014 telecommunications reform, the ban on charging rivals for network usage has been a significant drag on America Movil's profits.
Mexico's telecommunications regulator is discussing a proposal that would allow Slim to charge 0.03686 pesos for calls on its network, almost a third of what competitors can charge, Reuters reported on Tuesday.
One of America Movil's chief rivals in Mexico, AT&T, detailed its progress in the market on Tuesday.
The company said it closed the quarter with 13.8 million subscribers in Mexico, up 29 percent from the previous year, as revenue climbed 20 percent in local currency. ($1 = 18.1785 pesos as of Sept. 30)
America Movil closed at 18.19 pesos a share on Tuesday. The company released results after the market closed.
Additional reporting by Sheky Espejo; Editing by Cynthia Osterman and Peter Cooney