By Helen Reid

STOCKHOLM (Reuters) -H&M said unusually hot weather in many of its European markets had delayed the start of the autumn shopping season, sending sales lower in September, while cost cuts helped the fashion retailer's quarterly profit rise.

The decline deals a blow to hopes the world's second-biggest fashion retailer is turning its performance around after lagging behind Inditex, as a cost-of-living crisis curbs shoppers' spending.

"If the sales at your competitor basically go up by 14% with the same weather, that tells you something, to my mind," said Vera Diehl, portfolio manager at Union Investment, which holds shares in both H&M and Inditex.

H&M's shares rose 5% in early trade, however, as profits in the June-August quarter jumped and H&M stuck to a goal of increasing its operating margin to 10% next year and said its cost-cutting programme was continuing "at full speed".

In 2022, the margin was 3%. In the third quarter, the margin reached 8% from a year-earlier 2%.

The target is "challenging but achievable," Barclays analyst Nicolas Champ said, adding that it would, however, require some acceleration in top-line growth.

Operating profit in the Swedish group's third quarter jumped to 4.74 billion crowns ($431 million) from a year-earlier 902 million. Analysts polled by LSEG had on average forecast a 4.72 billion crown profit.

The year-ago figure included a one-off cost of 2.1 billion crowns for the group's exit from Russia, which also accounted for four percentage points of the 10% September sales decline.

"We believe H&M is very much in 'trading sales for profits' mode which is leading to margin improvement but some pressure on volumes," RBC analyst Richard Chamberlain said. "It appears to be losing some like-for-like share in major markets."

H&M announced a share buyback programme starting on Wednesday, planning to buy back up to 3 billion crowns of stock by March 31 next year.