US federal authorities have arrested a suspect following a spate of suspected pipe bombs sent to prominent Democrats and critics of US President Donald Trump are focusing on Florida, where they believe at least some of the 12 packages originated.
At least one person has been arrested, the Department of Justice said on Friday, without giving details.
Trump said that "these terrorising acts are despicable and have no place in our country".
"We will prosecute them, him, her, whoever it may be to the fullest extent of the law," he said in remarks at the White House.
Authorities have branded the parcel bombs acts of terrorism. They were sent less than two weeks before midterm elections that could alter the balance of power in Washington.
A police bomb squad and canine units joined federal investigators on Thursday to examine a sprawling US mail distribution centre at Opa-Locka, northwest of Miami, Miami-Dade County police said.
All the suspicious packages are believed to have gone through the US Postal System at some point, reported Reuters news agency, citing an unnamed federal law enforcement source.
According to the FBI, many of the packages had the return address of the Florida office of US Representative Debbie Wasserman Schultz, who formerly chaired the Democratic National Committee.
No one was reported injured and authorities intercepted several of the packages carrying the explosive devices before they reached their intended destinations. Along with the US Secret Service and the Bureau of Alcohol, Tobacco and Firearms (ATF), the FBI has launched a massive investigation into the incidents.
President Trump issued a condemnation at the White House on Wednesday, describing the incidents as "abhorrent" and "despicable".
On Thursday morning, however, Trump took to Twitter, apparently to blame the media for the attempted violence. He wrote that "a very large part" of anger in the US "is caused by the purposely false and inaccurate reporting" in mainstream media outlets.
His comments prompted widespread criticism, including condemnation from CNN President Jeff Zucker, who charged the Trump administration with "a total and complete lack of understanding … about the seriousness of their continued attacks on the media".
Who has been targeted?
Former US Secretary of State Hillary Clinton
A suspicious package sent to Clinton, Trump's Democratic rival in the 2016 presidential election, was found late Tuesday during an off-site mail screening, according to the Secret Service. Clinton said later her family was fine.
Former US President Barack Obama
The Secret Service uncovered a suspected explosive device sent to Obama's residence in the Kalorama district of Washington, DC, early on Wednesday during a screening. Officials said Obama was not at risk.
CNN, former CIA director John Brennan
New York City Police evacuated the Time Warner Building Wednesday after a suspicious package was found in the building's mailroom. The package was addressed to Brennan in care of CNN. Brennan is an outspoken Trump critic and a periodic contributor to the network.
Former Vice President Joe Biden
Two suspicious packages were sent to Biden in Delaware. They were intercepted at different mail facilities. Authorities said the packages were similar to those sent to the others.
Billionaire philanthropist and financier George Soros
A small bomb was found on Monday in a mailbox outside a New York home of billionaire financier George Soros, one of the world's biggest donors to liberal groups and causes. Soros, who was not at the property, is a constant target of hate by right-wing and far-right figures in the United States and Eastern Europe.
US Congresswoman Debbie Wasserman Schultz and former Attorney General Eric Holder
The building housing the Florida office of Wasserman Schultz, former chairwoman of the Democratic National Committee, was evacuated after a suspicious package was found, according to media reports. The package was addressed to Holder but Wasserman Schultz was named on the return address.
US Congresswoman Maxine Waters
The FBI said on Wednesday it was investigating two packages addressed to Waters, who had also said Capitol Police told her that her Washington office was a target.
Trump has railed against Waters in the past, calling her "an extraordinarily low IQ person" and claiming she supports violence.
In response to the packages, Waters called on the president to "take responsibility for the kind of violence that we are seeing for the first time in different ways".
Actor Robert De Niro
A suspicious package similar to those sent to Clinton, Obama and others had been addressed to Robert De Niro at property he owns in Manhattan's Tribeca neighbourhood, according to a New York Police Department source. De Niro has been critical of Trump, who in turn has criticised the actor.
Former Director of National Intelligence James Clapper
On Friday, authorities intercepted a package addressed to Clapper care of CNN at a post office in Manhattan. The package resembles those sent out earlier in the week, encased in a padded envelope with six stamps.
"This is not going to silence [the Trump] administration's critics," Clapper told CNN on Friday morning.
US Senator Cory Booker
Authorities caught the package addressed to New Jersey Democratic Senator Cory Booker at a mail processing facility in Opa-Locka, a city in southern Florida, on Friday. The FBI said the package resembled the others sent out earlier in the week.