CAIRO, Dec 4 (Reuters) - Yields on Egypt's three- and nine-month Treasury bills rose at an auction on Sunday, central bank data showed.

Yields on the 91-day bill increased slightly to an average of 18.240 percent from 18.186 percent at the last sale on Nov. 27.

Yields on the 266-day bill rose to an average of 18.602 percent from 18.475 percent at the last similar auction.

(Reporting by Nadine Awadalla; editing by Jason Neely) ((Nadine.Awadalla@thomsonreuters.com;))