U.S. Capitol Police say 11 persons, including a Capitol Police officer, fell ill Monday afternoon after an unknown substance was dispersed into the air in basement tunnels between the Longworth and Rayburn House office buildings on Capitol Hill.

Police say they don't know what the substance was. But they have ruled it not to be hazardous.

A police spokeswoman says the victims exhibited symptoms similar to how the body responds after inhaling mace or pepper spray, such as shortness of breath and eye irritation.

No one who become sick was transported to the hospital. All were treated at the site by Capitol doctors.

The back entrances to the Longworth building were flung open to help disperse the substance and hallways were closed off.

The Longworth and Rayburn buildings are the homes to hundreds of offices to US House members and are located just across the street to the U.S. Capitol.