FORT LAUDERDALE, Fla. -- Workers have returned inside an office building after they were evacuated when a suspicious package was discovered at U.S. Rep. Ron Klein's office.

The Fort Lauderdale Fire-Rescue Department Hazardous Materials Response Team (Hazmat) cleared the scene at 800 East Broward Blvd, in Fort Lauderdale about 3:30 p.m.

"The material tested positive as a biological substance twice. That can be anything from the flu to anthrax," Kathy Collins of the Fort Lauderdale Police Department said just after 1:30 p.m. when fire officials ordered the building evacuated.

Collins described the substance as a "glittery powder."

Further tests of the substance on the scene determined it was not a toxin such as anthrax, risen or botulism, said Ted Lawson of the city of Fort Lauderdale. The powder will be sent to a laboratory for further testing to determine what the substance was, he said.

"Earlier today, one of our staff members in our Broward County office opened a package that came in the mail, which contained suspicious content. As a precaution, we followed standard protocol procedures and contacted the Capitol Police, who instructed us to contact the Ft. Lauderdale police. After a brief evacuation, our staff is back in the Broward County office. Our staff members are safe, and no one has been harmed because of this incident," said Adrienne Elrod, a spokesperson for Klein.

Klein was in Washington, D.C., when the incident happened. None of the employees in Klein's office suffered any ill effects from being exposed to the powder, according to Elrod.

The FBI is investigating a letter that was included in the package that contained a death threat.