Signet Group plc, the world’s largest jewelry retailer, posted a 13.5% sales gain (to $507.2 million) for its first quarter, ending May 4. Comparable store sales of the London-based company rose 6.8%.

Sterling Jewelers Inc., the U.S. division, did $382.1 million in sales, or three-fourths of Signet’s total business. That represents a 15.1% gain.

Sterling’s comparable store sales went up 6.6%, thanks to “a greater level of marketing activity in the period,” said Terry Burman, Signet Group chief executive and chairman of Sterling. “This very encouraging performance [was] achieved against the background of continuing economic uncertainty.”

Signet’s United Kingdom division did $125.1 million in sales, an 8.8% increase. Its comp store sales grew 7.4%, aided by rising sales of “more aspirational products,” particularly diamonds and watches.

Formal first quarter earnings results will be announced on June 13.

Signet operated 1,639 specialty retail jewelry stores as of May 4, including 1,035 stores in the United States (where Sterling trades as “Kay Jewelers”, “Jared The Galleria Of Jewelry” and under a number of regional names), and 604 stores in the United Kingdom, including “H. Samuel,” “Ernest Jones” and “Leslie Davis.”

JCK