A law enforcement source tells The Associated Press that Miami-Dade police have gone to the mail-sorting facility in Opa-Locka, Florida, at the request of the FBI in connection with the suspicious package investigation.
The source says it was a precautionary measure.
The law enforcement source was not authorized to discuss an ongoing investigation and spoke on condition of anonymity.
Suspicious packages were sent to prominent critics of President Donald Trump.
Postal inspectors are searching mail facilities for packages matching the 10 sent over the last four days.
No new packages containing explosives have been identified since Thursday morning.
All the suspicious packages were believed to have gone through the U.S. Postal System at some point, the source said. Many of the packages had the return address of the Florida office of U.S. Representative Debbie Wasserman Schultz, who formerly chaired the Democratic National Committee, according to the Federal Bureau of Investigation.
Former Vice President Joe Biden and actor Robert De Niro on Thursday became the seventh and eighth intended targets of the bombs, none of which exploded.
The bombs have heightened what already was a contentious campaign season ahead of the Nov. 6 elections in which Trump's Republicans will try to maintain majorities in the Senate and House of Representatives. The episode has also called attention to the harsh rhetoric Trump wields against his rivals.
Trump condemned the bombs but later blamed the media, his frequent foil, for much of the angry tone.
No one has claimed responsibility and the FBI urged the public to report any tips and be vigilant. The FBI and New York police scheduled a briefing for 3:30 p.m. EDT (1930 GMT).
The pipe bombs discovered on Wednesday were similar to the ones sent to Biden and De Niro, a federal official told Reuters. Authorities described the devices as crude while security experts said their goal may have been to create fear rather than to kill.
FBI TO STUDY CNN BOMB
One of the bombs was sent to the New York headquarters of CNN, which Trump has frequently derided for its coverage of him, and the network said on Thursday the device was being taken in a bomb-proof truck to the FBI lab in Quantico, Virginia, for analysis.
In addition to the bomb, the package contained an envelope of white powder. CNN said initial tests deemed it was not anthrax but further examination was planned.
Leading Democrats said the bombs were a dangerous outgrowth of an antagonistic political atmosphere created by the president.
Trump and other Republicans have likened Democrats to an "angry mob," citing protests at the confirmation hearing of U.S. Supreme Court Justice Brett Kavanaugh.
The FBI said on Thursday one of the two packages sent to Biden - who once said he would have fought Trump if they were in high school - was discovered at a mail facility in his home state of Delaware and the second at another location.
The device intended for De Niro, who received a loud ovation when he hurled an obscenity at Trump at the Tony Awards in June, was sent to one of his properties in New York City.
At a Wisconsin rally on Wednesday night Trump, who has denounced news media organizations as an "enemy of the people," called attention to "how nice I’m behaving tonight” but on Thursday morning he attacked the media.
"A very big part of the Anger we see today in our society is caused by the purposely false and inaccurate reporting of the Mainstream Media that I refer to as Fake News," Trump wrote. "It has gotten so bad and hateful that it is beyond description. Mainstream Media must clean up its act, FAST!"
TWO BOMBS FOR WATERS
Several of the people who were sent bombs - including former President Barack Obama and Trump's rival for the presidency, Hillary Clinton - are frequent targets of right-wing critics.
Also sent packages were Eric Holder, who served as attorney general under Obama; former CIA Director John Brennan, who had his security clearance withdrawn after frequently lambasting Trump; prominent Democratic Party donor George Soros; and California Representative Maxine Waters, another outspoken Trump critic. Two packages were sent to Waters, whom Trump has called "an extraordinarily low IQ person."
Several politicians, including U.S. Senate Majority Leader Mitch McConnell and New York City Mayor Bill de Blasio, described the package bombs as an act of terrorism.
"Someone is trying to intimidate. Someone is trying to quash voices in this country using violence," De Blasio said. "I am confident that we will find the perpetrator or perpetrators."
Some major media outlets in New York, including the New York Times, increased security on Thursday.
New York Governor Andrew Cuomo told CNN some of the packages in his state were hand-delivered and that authorities were scrutinizing security camera videos for signs of the bomber.
Trump told the Wisconsin rally his government would conduct "an aggressive investigation."
"Any acts or threats of political violence are an attack on our democracy itself," Trump said. "We want all sides to come together in peace and harmony."
Last week, Trump heaped praise on a Montana congressional candidate who assaulted a reporter during his successful 2017 campaign.
The first package turned up on Monday and was addressed to Soros, the billionaire financier and advocate of liberal, open-border values who is a frequent target of right-wing conspiracy theories.
The FBI said on Wednesday the packages consisted of a manila envelope with a bubble-wrap interior containing "potentially destructive devices." Each bore a computer-printed address label and six "Forever" postage stamps, the FBI said.