The package was addressed to former presidential candidate Hillary Clinton at her New York home. (AP: Seth Wenig)
Suspected pipe bombs have been sent to Barack Obama, Hillary Clinton and other political figures who have been criticised by US President Donald Trump.
None of the devices exploded.
Here is what we know about the suspicious packages so far:
Who were the bombs sent to?
Hillary Clinton and Barack Obama were both sent explosive devices in the mail. (ABC News/ Facebook)
The list of Democratic figures who have been sent suspicious packages this week include former president Barack Obama, former presidential candidate Hillary Clinton, former attorney-general in the Obama administration Eric Holder, and Democratic congresswoman Maxine Waters, a vocal critic of Mr Trump.
Former CIA director John Brennan, who has been critical of Mr Trump, and billionaire philanthropist George Soros have also been targeted.
All of the packages had the return address of Democratic Florida congresswoman Debbie Wasserman Shultz.
Mr Holder’s package had the wrong address and was sent to Ms Wasserman Shultz’s office in Florida after the package could not be delivered to his address.
Ms Wasserman Shultz was the former chairwoman of the Democratic National Committee, but resigned from her position after the release of DNC emails during the 2016 US presidential election campaign.
Two packages were sent to Ms Waters.
At a news conference New York Governor Andrew Cuomo claimed that a device was sent to his office in Manhattan, but New York police and Mr Cuomo’s office later confirmed the device was not a suspicious package but a USB drive containing information on the far-right organisation the Proud Boys.
Debbie Wasserman Schultz’s Florida office was listed as the return address on the packages. (Reuters: Scott Audette)
How were they detected?
The package addressed to Mr Obama was intercepted by the Secret Service at the former president’s home in Washington.
The explosive package sent to Mrs Clinton’s New York home was discovered at a mail sorting facility, and did not reach the Clintons’ home. Former US president Bill Clinton was at home at the time the package was discovered while Ms Clinton was campaigning in Florida.
The Secret Service said both packages “”were immediately identified during routine mail screening procedures as potential explosive devices and were appropriately handled as such.”
The package addressed to Mr Brennan, which forced the evacuation of the Time Warner Centre in New York, was found in the CNN mail room. Mr Brennan is a frequent guest on CNN.
One of the packages addressed to Ms Waters was discovered at a congressional mail sorting facility in Maryland. Another was found in a Los Angeles postal facility.
New York Police Department’s bomb squad arrived at the Time Warner Centre after a suspicious package was found. (Reuters: Kevin Coombs)
Which package was found first?
Billionaire George Soros was reportedly not home at the time the device was found and detonated. (AP: Francois Mori)
A package containing what law enforcement believe was a small bomb was found in a mailbox outside the gates of billionaire philanthropist George Soros’ home on Monday, in the New York town of Katonah.
The suspected bomb was found by an employee at Mr Soros’ residence, who placed the package in a wooded area and immediately called police. Police alerted the FBI and the Bureau of Alcohol, Firearms and Explosives.
Mr Soros was not home when the bomb was discovered, and no one was injured.
A bomb addressed to “Former First Lady Hillary Clinton in Westchester County” was found the next day during screening away from the Clinton home while the remaining packages were discovered on Wednesday.
An alarm could be heard live on CNN shortly after 10:00am on Wednesday following the discovery of the suspicious package sent to Mr Brennan at the Time Warner Centre.
What was in the packages?
Law enforcement officials say the packages are similar manila envelopes with bubble-wrap interior packed with shards of glass, bearing six stamps and computer-printed address labels.
The packages sent to Mr Obama, Mr Brennan, Mrs Clinton, Ms Waters and Mr Holder all contained suspected pipe bombs.
The suspected pipe bomb sent to Mr Soros contained explosive black powder, and was believed to be delivered by hand.
A white powder was found during a search after the discovering of the suspicious package at the Time Warner Centre, according to New York police.
The devices have all been sent to an FBI lab in Virginia to be studied.
How have US political figures responded?
President Donald Trump responded to the news by saying threats of political violence had no place in the US, promising a full investigation into the packages.
“In these times, we have to unify, we have to come together, and send one very clear, strong, unmistakable message that acts or threats of political violence of any kind have no place in the United States of America,” Mr Trump said.
But he added: “The media also has a responsibly to set a civil tone and to stop the endless hostility and constant negative and oftentimes false attacks and stories”.
New York City Mayor Bill de Blasio called the package deliveries an “act of terrorism” at a press conference.
Mrs Clinton called the packages a sign of deep political divisions in the US, and stressed the need for the country to be united.
Democratic Senate and House leaders Chuck Schumer and Nancy Pelosi said Mr Trump’s words “rang hollow” in light of the President’s recent praise of a Republican congressman who body-slammed a reporter.
CNN chief Jeff Zucker criticised Mr Trump and the White House for what he called “a total and complete lack of understanding” about the seriousness of the Trump administration’s past attacks on the media.
What is the recent history of violence against US politicians?
Police and Secret Service agents reacting during the assassination attempt on US president Ronald Reagan. (AFP)
In October this year the US Secret Service confirmed it intercepted a suspicious envelope addressed to Mr Trump after authorities at a Pentagon mail screening facility found two envelopes suspected of containing ricin, a poison made from castor beans.
Those two envelopes were addressed to Defence Secretary Jim Mattis and the Navy’s top officer, Admiral John Richardson.
In 2011, Democratic Congresswoman Gabrielle Giffords survived being shot in the head with a pistol by Jared Lee Loughner in an attack which left six people dead in Arizona.
In the weeks following the attacks of September 11, 2001, anthrax spores were mailed to news media offices and two US senators, killing five people and infecting 17 others.
The most recent direct attack on a sitting US president happened in 1981, when Ronald Reagan survived an assassination attempt by John Hinckley Jr.