A handful of federal facilities in the Washington, D.C., area received packages on Monday that were considered suspicious, CBS News senior investigative producer Pat Milton reports.

Fort Belvoir, Fort McNair, Joint Base Anacostia-Bolling and the Naval Surface Warfare Center in Dahlgren, Virginia, all received the suspicious packages. The packages were each rendered "inert" by the facility's disposal units, although that does not mean that they were explosive. The packages sent to Joint Base Anacostia-Bolling and the Naval Surface Warfare Center are not believed to have contained any explosives.

The FBI is now in possession of the packages and is trying to determine if they were explosive and who sent them. The package sent to McNair, an Army base in Washington, D.C., tested positive for black powder and had a fuse attached.

"The FBI responded to multiple government facilities today for the reports of suspicious packages," the bureau said in a statement. "Each package was collected for further analysis by the FBI."

All government facilities have been screening everything coming into federal facility mailrooms, a source told CBS News. During screening, the packages were found to be suspicious, although it is unclear what made them suspicious.

It is also unclear whether each facility randomly found suspicious packages or whether an alert was sent out after one was found to be suspicious.