By Maarten van Tartwijk

AMSTERDAM--Koninklijke Ahold NV (AH.AE) on Thursday reported a sharp rise in fourth-quarter sales as the Dutch supermarket operator benefited from favorable currency effects and an extra selling week.

Sales were 9.8 billion euros ($10.7 billion) in the last three months of 2015, an increase of 21% compared with EUR8.1 billion in the same period a year earlier. Adjusted for the extra week and at constant exchange rates, sales rose 3.1%.

In the U.S., where Ahold generates the bulk of its revenue, sales at stores open at least a year excluding gasoline rose 1.6% and the company said its operating margin improved during the fourth quarter. In the Netherlands, sales at stores open at least a year rose 3.2%, thanks to a strong performance during the holiday season.

The results come as Ahold is working toward its planned merger with Belgium's Delhaize Group in a $29 billion tie-up that would create one of the largest supermarket operators in the U.S. The merger is expected to be completed by mid-2016.

-Write to Maarten van Tartwijk at maarten.vantartwijk@wsj.com

(END) Dow Jones Newswires

January 21, 2016 01:37 ET (06:37 GMT)