Clothing giant Gap Inc has reported flat comparable store sales for the month of December, dampened by lower demand at Old Navy.

The San Francisco-based retailer said comparable store sales increased 1% at Gap, were flat at Banana Republic, but slipped 2% at Old Navy.

Net sales reached US$2.05bn during the five weeks to 4 January, down 1.4% from $2.08bn in the same period of the prior year.

During the November and December holiday shopping period, Gap saw comparable store sales edge up 1%. Net sales grew 2% for the nine weeks to 29 December to $3.68bn from $3.59bn in the prior year period.

"We delivered solid overall performance across our global brands this holiday season, on top of last year's strong results," said chairman and CEO Glenn Murphy.