Leading US Muslim group receives hate mail with 'white powder'

The Washington headquarters of the largest US Muslim rights and advocacy group were briefly evacuated on Thursday after it received a "hate" letter containing a suspicious white powder that initial tests found to be harmless.

"Preliminary field tests indicate the substance is not dangerous," the Council on American-Islamic Relations, whose main office is three blocks from the US Capitol, said in a statement.

The letter is now in the hands of the Federal Bureau of Investigation for more extensive tests.

Three workers were temporarily quarantined because they came into contact with the substance. Other people in the office at the time were evacuated, but they have since been allowed back inside.

The letter "had a hate message," CAIR communications director Ibrahim Hooper told AFP, although at the request of authorities he declined to go into specifics of the message.

"We get fairly frequent death threats," Hooper added. "It's only when they come in this format that they go public."

"Local and federal authorities responded quickly and are currently investigating," CAIR wrote in a Facebook post.

"We are appreciative of their support. Alhamdulillah [praise God] no injuries have been reported thus far. Know that this will not intimidate or silence your civil rights lawyers and advocates. Today, we stand even more proudly in the face of increasing Islamophobia, prepared to protect your civil rights."

CAIR has been prominent in the media since Monday, when Republican presidential frontrunner Donald Trump called for a ban on all Muslims entering the United States.

The group broadly condemned the billionaire's proposal, and likened Trump to the "leader of a lynch mob".

The incident also comes a week after a married Muslim couple went on a rampage in San Bernardino, California, killing 14 people in what authorities are investigating as an act of terrorism.