DUBAI, July 29 (Reuters) - Zain, Kuwait's No.1 telecom operator by subscribers, reported a 34 percent fall in second-quarter profit on Wednesday, extending a sustained earnings slump.

The former monopoly, which operates in about eight countries in the Middle East and Africa, made a net profit of 39 million dinars ($128.8 million) in the three months to June 30, it said in a statement.

This compares with a profit of 58.8 million dinars in the year-earlier period, previous financial statements show.

Zain had posted falling profits in nine of the preceding 11 quarters as tougher domestic competition, service interruptions and higher costs in war-torn Iraq and foreign exchange volatility in other markets weighed on the bottom line.

Zain made a profit of 80 million dinars in the first half of 2015, down 30 percent from a year ago, the statement added.

($1 = 0.3027 Kuwaiti dinars)

(Reporting by Matt Smith; Editing by Olzhas Auyezov) ((matt.smith1@thomsonreuters.com; 00971506354039; Reuters Messaging: matt.smith1.thomsonreuters.com@reuters.net))