Supermarket chain Sainsbury\'s announced on Wednesday a modest rise in quarterly sales thanks to a record Christmas trading period for the group. The company, Britain\'s third-biggest supermarket chain after Walmart-owned Asda and the largest retailer Tesco, said that total sales in the 14 weeks to January 5 rose by 3.9 percent from the level for the equivalent period 12 months earlier. Sales at stores open for at least one year rose by a weaker 1.5 percent, Sainsbury\'s added in a statement. Chief executive Justin King said the week before Christmas was Sainsbury\'s \"strongest trading week ever, with customer transactions exceeding 27 million.\" He added: \"We expect the challenging economic backdrop to persist, with customers looking to re-balance their household budget after the festivities and so spending cautiously in the first few months of 2013.\"