By Sarah Young

LONDON (Reuters) -British sportswear retailer JD Sports posted a 2% fall in first-quarter sales and warned that higher prices in its key U.S. market from President Donald Trump's tariffs could hit customer demand, sending its shares down 6%.

JD, which makes nearly 40% of its sales in the United States through its Finish Line, Shoe Palace and Hibbett stores, warned in April that profits would only grow slightly, if at all, this year, even before any potential impact from tariffs.

The company is facing headwinds from a competitive and volatile market, worries over consumer spending and a drop-off in demand for Nike products, which account for 45% of its sales.

Shares in JD Sports slid 6% to 87 pence in early deals. The stock has lost 30% over the last 12 months, underperforming Britain's bluechip index, which is up 4%.

RBC analysts said the 2% drop in underlying sales for the 13 weeks to May 3 was softer than market expectations.

The group said on Wednesday that while it had limited visibility on the impact from tariffs, it was taking action by further diversifying the range of countries from which it sources goods.

The biggest potential impact would be a rise in the price of products for U.S. consumers, which could impact demand and dent confidence, JD warned.

"The tariff impact, though manageable, keeps us on hold," Panmure Liberum said, adding that current weakness was an opportunity for long-term investors.

JD, which also sells Adidas, On, HOKA and other sports brands from nearly 5,000 stores worldwide and online, did not on Wednesday give guidance for the current financial year. The consensus is for a 3% fall in pretax profit to 890 million pounds ($1.19 billion).

In the medium term, JD said it remained confident of delivering improved shareholder returns and said it was well positioned given its multi-brand model and focus on costs.

($1 = 0.7455 pounds)

(Reporting by Sarah Young, Editing by Paul Sandle, Kate Holton and Jan Harvey)