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* Q3 net loss 122 mln riyals vs loss of 144 mln riyals a year ago

* Q3 revenue 316 mln riyals

* Operator had 797,000 mobile subscribers as of Dec. 31

DUBAI, Jan 19 (Reuters) - Vodafone Qatar reported a narrower third-quarter net loss on Thursday partly on a rise in mobile subscribers, but the results missed analysts' estimates.

The firm, an affiliate of London-listed Vodafone (LSE: VOD.L - news) , made a net loss of 122 million riyals, according to Reuters calculations. This compares with a loss of 144 million riyals in the same period a year ago.

Two analysts forecast the firm, which starts its financial year on April 1, would post a quarterly loss of between 113 million and 119 million riyals, according to a Reuters survey.

Vodafone Qatar had 797,000 mobile customers as of Dec. 31, up 12 percent from a year ago. In the quarter, it added 15,000 subscribers.

"Vodafone Qatar has continued to deliver improved financial results to shareholders by growing its mobile customer base," Sheikh Abdulrahman bin Saud Al-Thani, Vodafone Qatar's chairman said in an emailed statement.

Vodafone Qatar, which ended Qatar Telecom's domestic monopoly in 2009, said revenue was 316 million riyals in the quarter, up from 267 million riyals a year earlier.

The operator will look to improve indoor coverage, increase data speeds and prepare to launch contract services in the fourth quarter, chief executive Richard Daly said in the statement.

Vodafone Qatar only offers pre-paid mobile contracts at present.

Its (Euronext: ALITS.NX - news) shares closed 0.4 percent lower on Qatar's bourse before the results were announced, ending at 7.52 riyals. The shares are 25 percent below its 2009 initial public offering price. (Reporting by Matt Smith; Editing by Amran Abocar)