A spokesman for a Muslim group says its headquarters on Capitol Hill have been evacuated after staffers came in contact with a suspicious substance that arrived in the mail.

Ibrahim Hooper tells The Associated Press that the headquarters for the Council on American-Islamic Relations was evacuated except for staffers who had come into contact with the substance.

Hooper says the substance arrived in an envelope Thursday morning.

Police in Washington confirmed they are investigating a suspicious package that was reported at the address for CAIR.

Alice Kim, a spokeswoman for the Metropolitan Police Department, said Thursday afternoon that police have blocked off the street where the building is located.