The White House has instructed US security agencies to review their training and policy materials for racial or religious bias after documents leaked by Edward Snowden revealed references to "Mohammed Raghead".
An investigation by The Intercept, the website co-run by former Guardian journalist Glenn Greenwald, revealed that the National Security Agency and the FBI spied on the e-mails of five prominent US activists and attorneys with Muslim backgrounds.
The Intercept cited the "Mohammed Raghead" epithet as a placeholder for a target in a surveillance training document from 2005.
The report, by Greenwald and Murtaza Hussain, suggested a persistent counterterrorism atmosphere in which Muslim heritage, faith or political activism attracted the scrutiny of US security agencies, despite first-amendment protections.
It presented the cases of five American activists and attorneys of Muslim heritage who appear to have been targeted for surveillance, at least between 2002 and 2008. None has been charged with a crime.
White House spokeswoman Caitlin Hayden said the administration took the accusations of the slurs extremely seriously.
"Upon learning of this matter, the White House immediately requested that the director of national intelligence undertake an assessment of intelligence community policies, training standards or directives that promote diversity and tolerance, and, as necessary, make any recommendations, changes or additional reforms," she said.
Hayden said that "the use of racial or ethnic stereotypes, slurs, or other similar language" was unacceptable. The government ordered a similar review of training material in 2011 after several training instructors told national security and military participants that mainstream Muslims supported violence.
The Intercept questioned whether the government obtained legal permission for its surveillance of the five targets of Muslim heritage.
It said its three-month investigation showed that "the system for authorising NSA surveillance affords the government wide latitude in spying on US citizens".
NSA and Justice Department officials this week denied that activists are targeted for criticising the government. While not discussing the individual cases, officials said Americans are only targeted for e-mail surveillance if there is probable cause.
The Guardian, Associated Press