Carrefour , Europe's No.1 retailer, issued a fresh profit warning on Thursday, citing an increasingly challenging economic climate.

The French group said it now expected 2011 operating profit to drop by between 15 percent and 20 percent against a previous forecast of a 15 percent decline.

The world's second-biggest retailer by sales after U.S. group Wal-Mart made the prediction after it eked out a 0.3 percent gain in third-quarter sales to 22.8 billion euros ($31 billion) as robust growth in emerging markets barely offset weak sales in France and western Europe.

Quarterly sales were broadly in line with a forecast of 22.74 billion euros in a Reuters poll of 12 analysts.

($1 = 0.725 Euros)

(Reporting by Dominique Vidalon; Editing by James Regan)