NEW YORK -- Newsweek has adopted new policies for the use of anonymous sources, a week after retracting a report that claimed investigators had found evidence the Quran was desecrated by interrogators at the U.S. naval prison at Guantanamo Bay.

In a letter to readers appearing in tonday's edition, Newsweek chairman and editor-in-chief Richard Smith apologized for the report and said the magazine will raise standards for anonymous sourcing.

"We got an important story wrong, and honor requires us to admit our mistake and redouble our efforts to make sure that nothing like this ever happens again," he wrote.

Two of the magazine's top editors will be assigned sole responsibility for approving the use of anonymous sources, and the magazine will stop using the phrase "sources said" to attribute information in stories, Smith said.

Newsweek retracted the May 9 report after officials at the White House, the Pentagon and the State Department criticized its publication and its use of an anonymous source.

The article said U.S. investigators had found evidence that interrogators placed copies of Islam's holy book in washrooms and had flushed one down the toilet to get inmates to talk. The magazine's report was blamed for violent protests in Afghanistan, where more than a dozen people died and scores were injured.

Rallies are planned for Friday in Pakistan and other countries to protest the report, with Islamic leaders calling on Pakistan's president, Gen. Pervez Musharraf, to abandon his support for President Bush's war against terrorism.

In the latest issue, the magazine stopped short of requiring that its reporters corroborate sources speaking on condition of anonymity with a second source, but Smith said that editors would work harder to do so.

"When information provided by a source wishing to remain anonymous is essential to a sensitive story -- alleging misconduct or reflecting a highly contentious point of view, for example -- we pledge a renewed effort to seek a second independent source or other corroborating evidence," Smith said.

The magazine also offered two new articles on the controversy in Monday's edition.

One story looks at an announcement this week by the International Committee of the Red Cross that Guantanamo detainees have made allegations of Quran desecration by U.S. soldiers, but none has been substantiated by the Pentagon.

The second article puts the Newsweek retraction in the context of other publications that have altered standards for anonymous sourcing following similar controversies.