Former United States President Barack Obama and former Secretary of State Hillary Clinton were among the targets of suspected package bombs delivered to several high-profile Democrats and CNN in what NewYork officials on Wednesday called an act of terrorism.

The suspicious parcels, at least five in all, were intercepted before any reached their intended recipients, including Obama's attorney general, Eric Holder, former CIA Director John Brennan and prominent Democratic Party donor George Soros.

The FBI said, two packages were sent to California Congresswoman MaxineWaters.

Joe Biden, a federal official said on Wednesday, "Investigators were trying to track down a suspicious package they believe was addressed to Obama's vice president".

None of the packages detonated, and nobody was hurt. There was no immediate claim of responsibility.

But news of the threats heightened tensions in a nation deeply polarized ahead of elections on Nov 6 that will decide whether Democrats take control of one or both houses of Congress from Republicans and deny President Donald Trump the majority his party now holds in both.

President Donald Trump condemned the series of attempted attacks on high-profile Democrats and others. President Donald Trump told a political rally in Wisconsin his government would conduct "an aggressive investigation."

"Any acts or threats of political violence are an attack on our democracy itself," Trump said. "We want all sides to come together in peace and harmony."

"Acts or threats of political violence have no place in the United States." Trump called the suspicious packages "despicable". Trump added a "major federal investigation" was underway.

He also said the media has a responsibility "to stop the endless hostility and constant negative and oftentimes false attacks and stories."

(Featured image: Reuters)