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WASHINGTON — At least one man has been arrested in connection with more than a dozen suspicious packages sent to government addresses on the Eastern Seaboard, most of them in the nation's capital, the FBI said Tuesday.

Tranh Cong Phan, 43, was arrested at his home in the Seattle area on Monday. He was scheduled to make his initial court appearance on Tuesday afternoon.

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Earlier Tuesday officials said they believed Phan sent a total of 12 packages to military and government addresses in the Washington metro area. But late Tuesday, the FBI's Washington field office appeared to leave open the possibility that more packages were mailed.

"It is possible that further packages were mailed to additional mail processing facilities in the Washington, D.C. metropolitan area," the FBI office said in a statement.

Officials have said packages turned up at the CIA's mail-sorting facility, a White House mail-sorting facility in suburban Washington, a Navy facility in Dahlgren, Virginia, and two facilities at Fort Belvoir, Virginia — the National Geospatial-Intelligence Agency and another defense university.

FBI investigators found that the packages contained potential destructive devices and appeared to have been sent by the same individual. Some of the packages included letters that one official described as disturbed and rambling.

The deliveries appeared to have been intended to cause fear rather than injure people or cause damage, one official said. But authorities have not confirmed a motive.

Prior to the FBI's statement late Tuesday night, Defense Secretary Jim Mattis told reporters earlier in the day that all of the packages mailed to Defense Department facilities were under the control of federal authorities.

"We've had nobody injured and all those packages and all the evidence is accessible and is the hands of the FBI right now."