Updated at 4:16 p.m.

The Council on American-Islamic Relations, the most prominent organization that tracks discrimination against Muslims in the United States, was evacuated Thursday afternoon due to a suspicious piece of mail.

Preliminarily, the substance does not appear to be dangerous, authorities concluded nearly two hours after the evacuation began.

Ibrahim Hooper, a spokesman for the organization, said that a poof of white powder wafted out of the envelope when a staff member opened it. He said that a letter with a hateful message was inside the envelope, and FBI officials planned to investigate the letter further.

A few people who came in contact with the powder were quarantined inside the building for first responders to check them out, and about 20 other employees who work at the organization’s headquarters on New Jersey Avenue SE went to wait outside, Hooper said.

“We get threats every day,” mostly online or by phone, Hooper said. “We don’t always get substances in the mail.”

He said the volume of threats has increased lately, starting with the Paris attacks and then further after the San Bernardino attack and then Donald Trump’s call for a temporary ban on Muslims entering the United States.

Related news: