The Apple logo shines inside of an Apple Store in New York July 19, 2010. REUTERS/Lucas Jackson

SAN FRANCISCO (Reuters) - Apple Inc said on Tuesday that it would delay release of its eagerly anticipated white iPhone again, this time until next spring.

The latest version of the popular handset, the iPhone 4, was released in June, but the white model was delayed first to July, then to the end of the year and now to early next year.

“We’re sorry to disappoint customers waiting for the white iPhone again,” Apple spokeswoman Trudy Muller. She declined to explain the delay.

Apple has never said exactly why the white iPhone has been so troublesome to produce. The company has only said the white model was “more challenging to manufacture than we originally expected.”

Rumors about the white iPhone have been on Apple-focused blogs for months, with explanations ranging from color-matching problems to an issue with the device’s backlight.

Color aside, Apple is not having any trouble selling its smartphone. The iPhone, which is available in black, has fueled Apple’s growth over the past few years.

IPhone unit sales rose 91 percent to 14.1 million in Apple’s most recent quarter, with a sales value of $8.6 billion.

Apple initially had trouble keeping up with demand, but the iPhone is now available in 89 countries.

Shares of Apple, based in Cupertino, California, fell 0.3 percent to close at $308.05.