The boost to US retailers from about $100bn of tax rebate cheques has proved short-lived, with leading chains on Thursday reporting sluggish or falling sales in July, while Wal-Mart warned of slowing sales ahead.

Wal-Mart, the largest US retailer, said it expected August sales in stores open at least a year to grow by between 1 and 2 per cent, after reporting 3 per cent sales growth in July.