A series of pipe bombs sent to high profile figures including Hilary Clinton and Barack Obama, and to CNN’s HQ, were packed full of shards of glass, an official has said.
X-ray images of the devices, made from PVC pipe about six inches long, revealed that they also contained small batteries and powder, according to the unnamed source.
The official was speaking on condition of anonymity to the Associated Press following the shocking incidents which saw a number of targets sent the bombs on Wednesday.
The FBI said the packages containing the explosives were sent to former president Mr Obama, the Clintons, former Attorney General Eric Holder, billionaire George Soros and CNN.
The targets of the bombs were some of the figures most frequently criticised by US leader Donald Trump.
New York City Mayor Bill de Blasio branded the shocking incidents as an effort to terrorise and “undermine our free press and leaders of this country through acts of violence”.
An investigation into the attempted attacks is under way and is “of the highest priority”, the FBI said after at least five suspicious parcels were intercepted on Wednesday.
There has been no immediate claim of responsibility.
A package addressed to Mr Obama was intercepted by Secret Service agents in Washington. A further package, confirmed to be a viable bomb, was intercepted by an aide at the Clintons' home in Chappaqua, New York.
Investigators believe the devices are of the same type that were sent to billionaire philanthropist and Remain-backer Mr Soros, a prominent Democratic Party donor.
The HQ of news broadcaster CNN was also evacuated after a suspicious package - later confirmed to be a pipe bomb - was found in its post room.
Police told NBC News that all four packages sent to the Time Warner Centre, Obama, Clinton and Soros are "nearly identical".
The White House condemned "the attempted violent attacks recently made against President Obama, President Clinton, Secretary Clinton, and other public figures".
Donald Trump later condemned the bomb threats, saying threats of political violence have no place in the US. He promised a full investigation.
The president said: “The full weight of our government is being deployed to conduct this investigation and bring those responsible for these despicable acts to justice. We will spare no resources or expense in this effort.”
