FBI Assistant Director William Sweeney would not confirm the origin of the packages Thursday, despite reports that investigators believe some came from Florida.

Several of the packages went through a US Postal facility in Opa-locka, Florida, two law enforcement officials familiar with the investigation said.

"Some were obviously in the postal system," Sweeney said. "I'll leave it at that."

The Miami-Dade Police Department tweeted that its bomb squad and K-9 Unit are providing assistance to federal partners at the USPS Opa-locka mail facility.

"This assistance is as a precautionary measure," it said. "We cannot provide additional information at this time due to the active nature of this federal investigation."