The California firm, which is due to release a new phone later this year, said it sold 50.8 million iPhones in the period, down 1% year-on-year.

Apple boss Tim Cook blamed a "pause" as customers wait for the next iPhone.

Shares in the firm fell nearly 2% in after-hours trading after earlier hitting a record high on expectations of better results.

Apple reported a 4.6% rise in revenue across the whole company to $52.9bn (£41bn), slightly below analysts' forecasts.

The dip in iPhone sales was offset by services, including Apple Pay, iCloud and the App store, which recorded an 18% increase in sales to $7bn.

Mr Cook also pointed to growth in sales of Apple Watch, as well as its AirPods and Beats earphones.

Despite falling unit sales, revenue from iPhones still climbed 1% to $33.2bn due to "robust" sales of its bigger, more expensive iPhone 7 Plus.