SARAJEVO, Oct 31 (Reuters) - Bosnia's second-largest telecoms firm, m:tel TLKM.BJ , posted third-quarter profit of 78.7 million Bosnian marka ($55 million) on Thursday, down 11 percent on lower revenue that the company said was due to a worsening economic situation. Revenues fell 3.2 percent to 356 million marka, with those from fixed-line down nine percent mainly due to unpaid bills, m:tel said in its consolidated financial statement on Thursday. M:tel said the worsening economic situation will most probably result in the reduced use of telecommunication services on the market of Bosnia's autonomous Serb Republic, where it mainly operates. "This will most probably reduce business activities of the Group, and ... expected revenues in 2013," m:tel said in the statement published on the website of the Banja Luka Stock Exchange (www.blberza.com). (1$=1.433 Bosnian marka) (Reporting by Daria Sito-Sucic; Editing by David Evans) ((daria.sito-sucic@thomsonreuters.com)(+38733 295 484)(Reuters Messaging: daria.sito-sucic.thomsonreuters.com@reuters.net)) Keywords: BOSNIA M:TEL/RESULT