N'DJAMENA, Aug 18 (Reuters) - Chad has fined a local subsidiary of Airtel 5 billion CFA francs ($8.3 million) for breaking investment commitments, saying an audit showed its network quality was deteriorating, the African country's telecoms regulator said on Friday.

Airtel Africa is based in the United Kingdom and operates in around a dozen countries in Africa. The company did not immediately reply to a request for comment.

The Chadian regulator said it had also issued a formal notice to the country's other main telecoms provider Moov Africa, owned by Maroc Telecom, over a degraded quality of service.

($1 = 599.2500 CFA francs) (Reporting by Mahamat Ramadane Writing by Nellie Peyton Editing by Jason Neely and Mark Potter)