The first letter was reported this afternoon at Mary Church Terrell Elementary School in south east Washington.
At least six of the letters, postmarked from Dallas, contained white powder, and a letter with the words 'AL AQEDA-FBI,' according to a bulletin released by the Washington Regional Threat and Analysis Center.
All the address labels had been typed and the letters were identical to those sent to District schools in October last year, the bulletin added.
Four of the letters have since been examined but no hazardous materials were found, a spokesman for the FBI said.
The agency is still looking at the others envelopes.
The letters had been mailed to schools around D.C., including Ronald H. Brown Middle School, whose principal told The Washington Post, that the school was preparing for an on-time dismissal.
Everything is OK,' Principal Darrin Slade said. 'Everything’s safe here. No problems.'
Pete Piringer, a spokesman for D.C. Fire and EMS, said some of the schools were evacuated for precautionary reasons. Read More