Suspicious packages have been sent to six government and military sites around the U.S. capital Washington, according to media reports Monday.

The FBI and military authorities said they were investigating a half-dozen suspicious packages which contained explosive components, NBC News reported. They were sent to military and intelligence addresses in the Washington area.

"On March 26, the FBI responded to multiple government facilities for the reports of suspicious packages. Each package was collected for further analysis by the FBI," the FBI said on Twitter.

The first was discovered Monday morning at the National Defense University, NBC reported.

Others turned up at the CIA's mail-sorting facility, a White House mail-sorting facility in suburban Washington, and a U.S. Navy facility in Dahlgren, Virginia, among others, according to NBC.

Among the facilities where the packages turned up were Fort McNair in the southwest District of Columbia and Fort Belvoir in Fairfax County, Virginia, both U.S. Army installations.

Law enforcement officials told the broadcaster the packages were sent through the post. Some included letters that one official described as disturbed and rambling.

The FBI is examining the parcels to see whether they are the work of the same person or persons, and to determine whether they were working devices or hoaxes meant to look real, according to NBC.

At Fort McNair, a suspicious package was delivered at about 8:30 a.m. eastern time, prompting officials to evacuate the building, according to a base spokesman.

Some four hours later a U.S. Army Ordnance Disposal unit confirmed that the package had tested positive for explosive residue and determined that a fuse was attached, the spokesman said.

Few details were released on the package found at Fort Belvoir, but a base spokesman said that it had been rendered safe.