Online fashion retailer ASOS posted a 20% rise in retail sales in the four months ended 30 June 2015 and said its sales for the full year should be at the higher end of its 15-20% guided growth range.UK growth remained strong at 27%, while international sales were up 16%, despite a number of currencies weakening against the pound, the company said.Revenue was up 21% year-on-year in the period to £396.7m and ASOS said the retail gross margin was around 280 basis points higher than the previous year.The number of active users rose 11% to 9.7m.In 2014, ASOS suffered from a costly warehouse fire that caused the company to cease trading for several days.ASOS CEO Nick Robertson said: "After accounting for our price investments during the period, the full year gross margin is nonetheless expected to remain in line with last year, assisted by tighter inventory control and strong full price sales."He added: "We have increased investment in our people and our customer proposition, particularly in relation to free returns trials. We therefore expect EBIT margin to remain at the guided level of around 4%."Numis Securities said it was a strong update, with gross margin "comfortably ahead of expectations".Despite the strong run in the shares, which are up 50% year-to-date, Numis retained it positive stance on the stock, encouraged by ASOS' unique customer proposition.