US retailers relied heavily on promotions to win over cautious consumers in June, and the trend may weigh on margins as they head into the key back-to-school shopping season.

Sales at stores open at least a year rose 3.1 per cent, shy of 3.2 per cent Wall Street predicted, according to 28 retailers tracked by Thomson Reuters.

The Standard & Poor's Retail Index fell 0.5 per cent, trailing the broader market.

'What it really says is we're just treading water,' said University of Pennsylvania's Wharton School marketing professor Stephen Hoch. 'There's no evidence that somehow the consumer is going to step up to the plate and spend us out of the economic doldrums.'

Teen apparel retailers like Abercrombie & Fitch and Hot Topic were among the best performers, along with department store chains from Macy's Inc to JC Penney. The companies benefited from warmer weather and promotions for Memorial Day.

Penney cited brisk sales of men's summer apparel ahead of Father's Day as well. Apparel retailer Gap and discount chains posted some of the weakest results.

June marked the 10th consecutive month of rising sales after a year of declines.-Reuters