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.

Support free-thinking journalism and attend Independent events

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.

Joe Biden and Barack Obama through the years Show all 15 1 /15 Joe Biden and Barack Obama through the years Joe Biden and Barack Obama through the years Joe Biden and Dr Jill Biden watch Barack Obama's farewell speech on 11 January. Obama called Biden his 'brother' Joe Biden and Barack Obama through the years US President Barack Obama speaks alongside US Vice President Joe Biden about the Affordable Care Act AFP/Getty Images Joe Biden and Barack Obama through the years Vice President Joe Biden and President Barack Obama Getty Joe Biden and Barack Obama through the years President Obama listens to Joe Biden speak of his work on defeating cancer on 18 October in the White House Reuters Joe Biden and Barack Obama through the years U.S. President Barack Obama is applauded by House Speaker Paul Ryan and Vice President Joe Biden while delivering his final State of the Union address to a joint session of Congress in Washington Reuters Joe Biden and Barack Obama through the years U.S. Vice President Joe Biden interjects as President Barack Obama delivers remarks at a reception for the 25th anniversary of the White House Initiative on Educational Excellence for Hispanics at the White House in Washington REUTERS Joe Biden and Barack Obama through the years Obama and Vice President Joe Biden react after a heckler was removed for their extended interruption (Reuters) Joe Biden and Barack Obama through the years U.S. President Barack Obama shakes hands with Speaker of the House John Boehner (R) as Vice President Joe Biden looks on Joe Biden and Barack Obama through the years Barack and Michelle Obama and Vice-President Joe Biden observing a moment of silence outside the White House to mark the 13th anniversary of the 9/11 attacks Getty Images Joe Biden and Barack Obama through the years Barack Obama and Joe Biden putt on the White House putting green Getty Joe Biden and Barack Obama through the years President Barack Obama and Joe Biden in April 2013 AFP/Getty Images Joe Biden and Barack Obama through the years January 1, 2013: U.S. President Barack Obama winks as he arrives with Vice President Joe Biden (L) in the briefing room Reuters Joe Biden and Barack Obama through the years President Barack Obama, Vice President Joe Biden and others receive an update on the mission against Osama bin Laden in the Situation Room of the White House May 1, 2011 in Washington, DC Getty Images Joe Biden and Barack Obama through the years Vice-President Joe Biden, right, confirmed that the US was looking at ways of taking legal action against Julian Assange - back in December 2010 GETTY IMAGES Joe Biden and Barack Obama through the years Joe Biden, left, and retired military officers watch President Barack Obama sign orders to close down the detention centre at Guantanamo Bay, Cuba, in January 2009 GETTY IMAGES

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.