The targets have all been high-profile critics of President Donald Trump.
None of the devices have exploded.
The FBI said the packages found so far had shared characteristics, including manila envelopes with bubble-wrapped interiors.
The USPS operates an innovative imaging system that photographs each piece of mail processed throughout the country. Even with the sender still unknown, politicians from both parties used the moment to decry a toxic political climate and lay blame.
"It's become so bad tempered and spiteful that it is beyond all description", he added. "Mainstream Media must clean up its act, FAST!"
Authorities had intensified their hunt for a serial mail bomber in recent days after suspected explosives were delivered to a string of political figures and others who have publicly criticized President Trump. Maxine Waters and Debbie Wasserman-Schultz, Democratic Sen.
One of the packages was recovered at a South Florida office of Rep.
"The linguist in me noticed that Debbie Wasserman Schultz, the last name is spelled missing a "c" and John Brennan's name is spelled missing an "n" and that kind of surprised me and I have a feeling that was done on objective to make this look like somebody who doesn't really know who these people are and that it wasn't an honest mistake". At least one contained projectiles, including shards of glass, a law enforcement official told CNN. The official said the devices were made from PVC pipe and covered with black tape. A retired police officer discovered the package, but initially didn't think anything of it and left it in his office.
The FBI, which is leading the investigation into the packages, has only confirmed the existence of 11 packages and has not released any information about suspects or any potential motivation for the mailings.
The packages were "clearly an effort to terrorize people politically, to choose people for political purposes and attack them due to their beliefs", New York City Mayor Bill de Blasio said.
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"It was addressed to Robert De Niro and is similar packaging to the others". The actor dropped an expletive insult at Trump at this year's Tony Awards and also apologized to Canadians for the "idiotic behaviour of my president". They said investigators searching for more suspicious parcels had not found any during the previous eight hours.
The packages, containing devices that appear to be explosive devices, began to show up on Monday, starting with billionaire George Soros, a major donor to Democrats and Democratic causes.
The devices sent to Clinton, De Niro, Obama, the CNN offices and Waters' East Coast office are either with the Federal Bureau of Investigation or headed to the agency's lab in Quantico. The package was "safely removed" from the post office, police said. They bore the return address of Florida Rep.
Regardless, investigators were treating the devices as "live" explosives New York City Police Commissioner James O'Neill said.
The packages are the latest to be sent to prominent Democrats and critics of President Donald Trump that were discovered earlier this week.
"Let's get along", he said at a Wisconsin rally on Wednesday night. "Have you ever seen this?"
Later, Trump was asked about the apparent support for him expressed by the suspect on social media and on his van, which bears an illustration that appears to depict Trump standing on a tank holding a rifle before an American flag with fireworks exploding in the background.
"We must never allow political violence to take root in America", Trump said at one point.
At an event in Texas on Wednesday, Mr Brennan criticised Mr Trump for his frequent inflammatory rhetoric.
The FBI had been conducting a nationwide manhunt for the perpetrator sending the pipe bomb packages.
The 88-year-old is one of the world's richest men and supported Clinton in 2016.
Authorities appealed to the public for tips at a Thursday afternoon news conference in NY.