Open this photo in gallery Law enforcement personnel operate a bomb disposal robot outside a post office which had been evacuated in Wilmington, Del., Oct. 25, 2018. MARK MAKELA/Reuters

Investigators looking at a series of pipe bombs zeroed in on a Florida postal facility as the number of explosive devices mailed to opponents and critics of U.S. President Donald Trump reached 12.

Three devices – two addressed to former vice-president Joe Biden in Delaware and one to actor Robert De Niro’s Manhattan restaurant – were recovered on Thursday. The Federal Bureau of Investigation confirmed that all of the packages resembled the seven previously intercepted since Monday, which had been mailed to former president Barack Obama, former secretary of state Hillary Clinton and left-wing billionaire George Soros, among others.

By Friday morning, two further suspicious packages had been found, one in Florida addressed to New Jersey Democratic Senator Cory Booker and one at a New York City post office. The New York City package was addressed to James Clapper, the former director of national intelligence, CNN reported.

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The FBI focused on a mail-sorting facility in Opa-locka, near Miami, which is believed to have processed at least some of the packages. Miami-Dade police said on Thursday evening they had also dispatched a bomb squad and K-9 unit as a “precautionary measure.” The FBI has repeatedly warned of the possibility more bombs are still in circulation.

U.S. bomb scares: What we know so far about attempted attacks on Clinton, Obama, CNN and others

Wednesday: Sent to John Brennan at CNN offices in NY NEW YORK Monday: George Soros residence in Katonah, NY Friday: Package found addressed to James Clapper Tuesday: Clinton home in Chappaqua, NY MANHATTAN Thursday: Building associated with Robert De Niro NEW JERSEY Long Island 0 1 KM Philadelphia Thursday: Package addressed to Biden intercepted at a mail facility in New Castle, Delaware MARYLAND Baltimore D.C. Atlantic Ocean DELAWARE Wednesday: Sent to Obama and Maxine Waters, intercepted at mail facility in Washington area 0 55 KM MURAT YÜKSELIR AND JOHN SOPINSKI / THE GLOBE AND MAIL, SOURCE:TILEZEN; OPEN- STREETMAP CONTRIBUTORS; HIU; NEW YORK TIMES; CNN Wednesday: Sent to John Brennan at CNN offices in NY NEW YORK Monday: George Soros residence in Katonah, NY Friday: Package found addressed to James Clapper Tuesday: Clinton home in Chappaqua, NY MANHATTAN Thursday: Building associated with Robert De Niro NEW JERSEY 0 1 Long Island KM Philadelphia Thursday: Package addressed to Biden intercepted at a mail facility in New Castle, Delaware MARYLAND Baltimore D.C. Atlantic Ocean DELAWARE Wednesday: Sent to Obama and Maxine Waters, intercepted at mail facility in Washington area 0 55 KM MURAT YÜKSELIR AND JOHN SOPINSKI / THE GLOBE AND MAIL SOURCE:TILEZEN; OPENSTREETMAP CONTRIBUTORS; HIU; NEW YORK TIMES; CNN Wednesday: Sent to John Brennan at CNN offices in NY NEW YORK Monday: George Soros residence in Katonah, NY Friday: Package found addressed to James Clapper, the former director of national intelligence MANHATTAN Tuesday: Clinton home in Chappaqua, NY Thursday: Building associated with Robert De Niro 0 1 KM Long Island NEW JERSEY Philadelphia Thursday: Package addressed to Biden intercepted at a mail facility in New Castle, Delaware MARYLAND Baltimore Wednesday: Sent to Obama and Maxine Waters, intercepted at mail facility in Washington area Atlantic Ocean DELAWARE 0 55 D.C. KM MURAT YÜKSELIR AND JOHN SOPINSKI / THE GLOBE AND MAIL, SOURCE: TILEZEN; OPENSTREETMAP CONTRIBUTORS; HIU; NEW YORK TIMES; CNN

Thursday: Package addressed to Maxine Waters intercepted at a mail facility in Los Angeles CANADA U.S. Calif. Fla. Gulf of Mexico MEXICO 0 500 KM Wednesday: Suspicious packages found addressed to Eric Holder at Rep. Debbie Wasserman Schultz’s offices in Sunrise Friday: Package found addressed to New Jersey Democratic Senator Cory Booker MURAT YÜKSELIR / THE GLOBE AND MAIL, SOURCE: TILEZEN; OSM CONTRIBUTORS; HIU; WIRES Thursday: Package addressed to Maxine Waters intercepted at a mail facility in Los Angeles CANADA U.S. Calif. Fla. Gulf of Mexico MEXICO 0 500 CUBA KM Wednesday: Suspicious packages found addressed to Eric Holder at Rep. Debbie Wasserman Schultz’s offices in Sunrise Friday: Package found addressed to New Jersey Democratic Senator Cory Booker MURAT YÜKSELIR / THE GLOBE AND MAIL, SOURCE: TILEZEN; OPENSTREETMAP CONTRIBUTORS; HIU; WIRES CANADA Thursday: Package addressed to Maxine Waters intercepted at a mail facility in Los Angeles Wednesday: Suspicious packages found addressed to Eric Holder at Rep. Debbie Wasserman Schultz’s offices in Sunrise U.S. Calif. Fla. MEXICO Gulf of Mexico Friday: Package found addressed to New Jersey Democratic Senator Cory Booker 0 500 KM MURAT YÜKSELIR / THE GLOBE AND MAIL, SOURCE: TILEZEN; OPENSTREETMAP CONTRIBUTORS; HIU; WIRES

All of the parcels listed Congresswoman Debbie Wasserman-Schultz’s Miami-area office as the return address.

None of the bombs exploded. The ones addressed to Mr. Obama, Ms. Clinton, Mr. Biden and Democratic Congresswoman Maxine Waters were intercepted before delivery. Those sent to Mr. Soros, Mr. De Niro and former Central Intelligence Agency director John Brennan – care of CNN’s Manhattan headquarters – reached their destinations but were flagged by the recipients, who called authorities. One mailed to former attorney-general Eric Holder was sent to Ms. Wasserman-Schultz’s office.

Mr. De Niro has long been critical of Mr. Trump. During the presidential election, he recorded a video in which he said Mr. Trump was “a fool” and “a bozo” and said he would like to punch him in the face. Mr. De Niro also used profane language to disparage Mr. Trump at the Tony Awards this past June.

Mr. Booker is often touted as a potential 2020 presidential candidate. Mr. Clapper, who oversaw the U.S. intelligence community under Mr. Obama, has been critical of Mr. Trump. Both he and Mr. Brennan are the frequent target of conspiracy theorists – often encouraged by the President – who claim that a secretive “deep state” of intelligence agents spied on Mr. Trump’s presidential campaign and has tried to thwart his administration.

On Wednesday afternoon, Mr. Trump had called for unity and said he was “upset” by the attacks. But by Thursday, he was pinning blame for the country’s increasingly fraught political divide on the media – even as a cable-news outlet was one of the targets.

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“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,” the President tweeted. “It has gotten so bad and hateful that it is beyond description. Mainstream Media must clean up its act, FAST!”

White House press secretary Sarah Huckabee Sanders, accused CNN of blaming Mr. Trump for the bombing campaign and indicated he would not be dialling back his rhetorical attacks on political opponents.

“Ninety per cent of the media attention around this President is negative,” she told reporters at the White House. “The very first thing your network did is come out and accuse the President of being responsible for [the bombs.]”

Mr. Trump last week cheered a Republican congressman convicted of body-slamming a newspaper reporter and has in the past tweeted a video of himself beating up a man with a CNN logo superimposed over his head taken from a 2007 WWE broadcast.

CNN’s parent company, AT&T, on Thursday announced a US$250,000 donation to the Committee to Protect Journalists.

“Threats to journalists are, at the very core, threats to freedom and liberty,” AT&T chief executive Randall Stephenson said in a statement.

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Lara Schwartz, a political-communications expert at American University in Washington, said the response to the attempted bombings was more divided than at other such moments in the country’s history. After the Sept. 11, 2001, attacks for instance, Ms. Clinton and then-New York mayor Rudy Giuliani – who had nearly squared off against each other for a Senate seat – were seen side-by-side at the site of the World Trade Center. And Al Gore, who had narrowly lost the previous year’s presidential election to George W. Bush, declared his former rival “my commander-in-chief” and urged fellow Democrats to rally behind him.

“If ever there was a moment for people who are engaged in battle to model unity, it would be when someone is targeting people like this,” Prof. Schwartz said in an interview. “It seems we are not there now. We should all be noting how huge that is.”

Prof. Schwartz contended Mr. Trump is reflecting a broader cultural and political shift: As congressional districts have been gerrymandered into safe seats and politicians have turned to increasing ideological purity to motivate their bases, the incentive to battle the other side rather than work with it has grown. And media is similarly fragmented, with different outlets telling different stories and a substantial chunk of the President’s base believing it would be a good idea to shut down outlets they do not agree with.

“A whole lot of people are ready to believe that the media is the enemy,” she said.