Specialty clothing retailer Gap Inc has booked an 8% increase in January comparable store sales thanks to continued momentum in its North American businesses.

The San Francisco-based retailer said net sales reached US$1.13bn for the five-week period to 2 February, compared with $833m in the same period last year.

Comparable sales were up at all of its North American brands, with Gap and Banana Republic each recording an 8% gain and Old Navy posting 12% growth. International comparable sales climbed 1%, reversing a 10% decline a year ago.

"We're pleased with the continued momentum in the business across all our brands in North America," said chairman and chief executive officer Glenn Murphy. "As we transition to 2013, our focus remains on delivering compelling product in order to sustain our positive sales performance."

Meanwhile, fourth-quarter net sales increased 10.5% to $4.73bn, up from $4.28bn last year, while comparable sales were up 5%. Full-year sales rose 7.6% to $15.65bn against $14.55bn the year before, and comparable sales climbed 5%.

Gap expects fourth-quarter diluted earnings per share to be in the range of $0.70 to $0.71. In addition, it now expects year-end inventory dollars per store to be slightly higher than previous guidance, driven by higher in-transit inventory due to the earlier Easter holiday in 2013.