(Reuters) - U.S. jeweler Tiffany & Co (>> Tiffany & Co.) reported a 6 percent jump in sales at stores open at least a year during the holiday shopping period, helped by strong demand in America.

The company, famed for its blue boxes and its Fifth Avenue flagship store in Manhattan, maintained its full-year profit forecast, in contrast to other large retailers that have slashed their outlooks due to steep discounts.

Tiffany said net sales rose 8 percent in November and December, a period that can account for a third of annual sales and almost half of profit.

Lower-end peer Zale Corp (>> Zale Corporation) reported a 2 percent rise in comparable-store sales for the same period, driven by higher sales at its Zales Jewelers and Zales Outlet stores.

Zale's shares rose 17 percent to $16.53, while Tiffany's shares were slightly lower at $91.93 in early trading on the New York Stock Exchange.

Tiffany said sales in the Americas, which accounts for nearly half of total revenue, rose 6 percent in the two months ended December 31. Sales rose 5 percent in Asia, excluding Japan.

"They put some new products into the marketplace and they put money behind marketing and advertising them and that seems to be working", said Edward Jones analyst Brian Yarbrough.

Tiffany also maintained its full-year profit forecast of $3.65 to $3.75 per share, excluding items.

Signet Jewelers Ltd  (>> Signet Jewelers Ltd.), the largest U.S. jeweler, on Thursday estimated fourth-quarter profit that missed analysts' estimates as increased promotions hurt margins.

The parent of Kay Jewelers and Jared reported a 5 percent rise in same-store sales as UK and online sales improved.

Signet's shares fell 1 percent to $72.86 on Friday.

(Reporting by Siddharth Cavale and Devika Krishna Kumar in Bangalore and Phil Wahba in New York; Editing by Savio D'Souza)

Stocks treated in this article : Signet Jewelers Ltd., Tiffany & Co., Zale Corporation