Former US vice president Joe Biden is the latest high-profile Democrat figure believed to have been sent a bomb through the post, following a spate of similar incidents in which Barack Obama, Hillary Clinton and CNN were also targeted.
The secret service intercepted the packages addressed to Mr Obama and Ms Clinton, but CNN’s New York office was evacuated after a “live explosive device” addressed to former CIA director John Brennan was discovered on the premises.
Meanwhile New York governor Andrew Cuomo received a similar device at his office in Manhattan, two devices intended for California Democratic representative Maxine Waters were intercepted at a mail screening facility in Maryland, and newspaper The San Diego Union-Tribune evacuated its offices after suspicious packages were found.
Prominent Democratic Party donor George Soros, and Mr Obama’s attorney general Eric Holder were also targeted in similar incidents.
Late on Wednesday night, the FBI said they were trying to track down a parcel intended for Mr Biden.
The parcel was reportedly misaddressed and returned to sender, but is now considered suspicious due to similarities to other incidents.
“So far the devices have been what appeared to be pipe bombs,” John Miller, the New York City police deputy commissioner for intelligence and counterterrorism, told a news conference.
An FBI-led Joint Terrorism Task Force of federal, state and local law enforcement agencies “will continue to work to identity and arrest whosoever is responsible for sending these packages,” FBI Director Christopher Wray said in a statement.
The FBI investigation is being treated as a domestic terror matter.
The spate of incidents unfolded rapidly on Wednesday. None of the eight packages detonated and nobody was injured, but there was also no claim of responsibility for the attacks.
But questions immediately began being asked about the motives of those responsible for sending the devices.
The bomb threats have heightened tension in a nation deeply polarised ahead of the midterm elections on 6 November, in which Donald Trump’s Republicans are at risk of losing their majority in the House of Representatives.
Some Democrats were quick to accuse the president himself of stoking the potential for political violence by frequently engaging in hyper-partisan, vitriolic rhetoric.
Mr Trump condemned the attacks, telling a political rally in Wisconsin on Wednesday his administration would conduct “an aggressive investigation”.
“Any acts or threats of political violence are an attack on our democracy itself,” Mr Trump said. “We want all sides to come together in peace and harmony.”
But he also said the media has a responsibility “to stop the endless hostility and constant negative and oftentimes false attacks and stories.”
His remarks prompted a standing ovation.
Agencies contributed to this report
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