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Shares in Slim's America Movil slump after weak results

(Adds details from conference call and context)

MEXICO CITY, April 28 (Reuters) - Shares in Carlos Slim's America Movil slumped more than 9 percent on Thursday, a day after the telecoms company posted results which missed expectations by a wide margin, prompting analysts to downgrade their ratings.

Profit dropped more than 40 percent in the first quarter, the company reported on Wednesday, saying mobile competition in Mexico from rivals like AT&T Inc. intensified and it shed subscribers in Brazil.

The company's share price was down 9.09 percent at 12.4 pesos per share at 10.35 a.m. local time (1535 GMT).

In 2013, Mexico passed a telecoms law aimed at curbing America Movil's 70 percent mobile market share by forcing it to share cell towers and other equipment with rivals, and letting them connect calls to its network for free.

The company's margin on earnings before interest, tax, depreciation and amortization (EBITDA) at home has fallen every quarter since the reform was fully implemented. It hit a new low of 35.7 percent in the first quarter.

Analysts at brokerages Intercam and Banorte Ixe both downgraded their ratings on the company to "sell" after the results.

America Movil's Chief Executive Officer Daniel Hajj said on a conference call on Thursday that competition in the Mexican market had become much more aggressive in recent months, with prices now much lower than in the United States.

"Eventually things are going to be more rational in terms of promotions," Hajj said. He added that he expects the company to lose market share in Mexico wireless over the next few years.

Mexico's telecoms regulator is currently reviewing the measures in place against the company under the law, but will not present results until November.

(Reporting by Christine Murray; Editing by David Gregorio)