"We've recently heard from many loyal Apple customers who were disappointed to learn that we had removed our products from the EPEAT rating system. I recognize that this was a mistake. Starting today, all eligible Apple products are back on EPEAT," Bob Mansfield, Apple's senior vice president of hardware engineering, said in a letter posted on the company's website.

"It's important to know that our commitment to protecting the environment has never changed, and today it is as strong as ever," said Mansfield in the letter.

"Our relationship with EPEAT has become stronger as a result of this experience," said Mansfield, adding that Apple looks forward to working with EPEAT to help its system "evolve."

Robert Frisbee, EPEAT's chief executive officer, said the organization will "look forward to Apple's strong and creative thoughts on ongoing standards development."

Last Friday, EPEAT told technology news service CIO Journal that Apple had pulled its 39 certified desktop computers, monitors and laptops from the system and gave no reason for its withdrawal.

EPEAT focuses on hardware recycling rather than other environmental standards like carbon emissions. The organization said Apple had not submitted the latest MacBook Pro with the high- resolution Retina display, which was introduced in June, for certification.

According to iFixit.com, a site publishing free online repair guide for electronic products, Apple's current design direction is in conflict with EPEAT's requirement for "disassemble-ability," an important consideration for recycling.

In a new MacBook Pro teardown, iFixit said Apple's latest laptop is nearly impossible to fully disassemble as the battery is glued to the case and the display to the back.

On Tuesday, San Francisco city officials said they are planning to block purchases of Apple computers by all its municipal agencies, noting that they hope Apple will reconsider its participation in the system.

Administrators at University of California, Berkeley, and Cornell University also said they are reviewing their purchases from Apple.

In a statement issued Friday after Apple's announcement, Melanie Nutter, director of San Francisco Department of the Environment, said that the department "is pleased to learn that Apple is rejoining EPEAT."

"Independent standards, eco-labels, and registries like EPEAT are critical tools for verifying the environmental integrity of products for consumers," Nutter noted.

The EPEAT system is founded in 2006 through funding by the U.S. federal Environment Protection Agency and manufacturers, including Apple, to certify products that are recyclable and designed to maximize energy efficiency and minimize environmental harm.

In 2007, former U.S. President George W. Bush issued an executive order to require 95 percent of computers in federal government agencies to be EPEAT-certified. Around 70 percent of U. S. universities require EPEAT-only computers, according to EPEAT.