New York City -- Barnes & Noble reported a preliminary same-store sales increase of 9.7% for the nine-week period ended on Jan. 1, led by the popularity of its Nook e-readers (the figure includes Nook devices sold in stores but not on its website). Last week, Barnes & Noble said the Nook had become its best-selling single item ever.

Barnes & Noble, which put itself up for sale in August, introduced the Nook in 2009 in a bid to compete with Amazon.com's market-leading Kindle and win a share of the growing digital books market.

Barnes & Noble also said it set a company retail sales record on Dec. 23. The retailer said it would release more detailed sales figures on Thursday.