The company said its eagerly anticipatediPhone was on schedule to ship in late June as planned after passing several of its required certification tests.

But it said delivering the phone on time contributed to the delay of the next version of its OS X operating system, code-named Leopard, until October because the company said it had to divert resources to the iPhone.

"iPhone contains the most sophisticated software ever shipped on a mobile device, and finishing it on time has not come without a price -- we had to borrow some key software engineering and ... resources," Apple said in a statement.

Tim Bajarin, an analyst with Creative Strategies in San Jose, California, said the delay in Leopard could slow the pop in sales that normally comes from die-hard Apple computer fans, who will now likely wait to buy new computers.

"I actually think the effect is going to be somewhat negligible," Bajarin said.

Leopard is expected to boast new features including a file back-up feature called "Time Machine" and improvements to its e-mail and instant messaging software. Another feature allows users to move from their standard desktop view to an archival view showing every change made to a particular file.

Apple said Leopard's features would be complete in early June ahead of its worldwide developers conference but that the product would not be ready for release. Instead, the company said it plans to give developers a test copy and ship Leopard in October.

The delay follows Apple's January debut of its much-anticipated take on the smart phone, combining a phone, an iPod and instant messaging in a sleek device with a large screen.

Analysts have said the iPhone is a potentially huge source of growth as Apple seeks new revenue streams and ways to build on its 70 per cent-plus U.S. market share for digital music players.

Apple shares fell nearly 3 percent in extended trade to $89.51 from a Nasdaq close of $92.19.

© Reuters