A number of people have been injured by a suspected tear gas attack in Germany. Eyewitnesses report that the incident happened check-in area at Terminal 1 of the the country’s busiest airport, Frankfurt. Six people were being treated for breathing problems, according to the police. "The cause is unclear, investigations continue," a spokesperson added. Frankfurt Airport operators said the fire brigade's operations had ended and found no "harmful substance" in the departures hall. The cause of the incident is not know and Frankfurt Airport representatives reported that "no harmful substance [has been] found".