The US President has launched another attack on the media, hours after calling for ‘unity’ in the face of threats of “political violence of any kind.”

Donald Trump was speaking after mail bombs were sent to the offices of CNN and several high-profile political rivals.

At least seven suspicious packages have now been identified - with recipients including former president Barack Obama and Hillary Clinton.

The FBI has said it is also trying to track down a suspicious package it believes was addressed to former vice president Joe Biden.

Billionaire George Soros - who funds a number of progressive causes, and is a frequent target of right-wing criticism and conspiracy theories - was the first to receive a "potentially destructive" package on Monday.

US officials have said the devices were packed with glass.

They did not detonate and were intercepted before they reached their targets.

US President Donald Trump speaks during a rally in Wisconsin, 25-10-2018. Image: Mike Roemer/AP/Press Association Images

Speaking at a rally in Wisconsin yesterday evening, President Trump said "any acts or threats of political violence are an attack on our democracy itself."

The president, who has labelled large parts of the press "enemies of the people," said the media has "a responsibility to set a civil tone and to stop the endless hostility."

Earlier that evening, he said that, “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."

All of the targets of the attack are frequently criticised by right-wing politicians and pundits - including Mr Trump, who regularly describes CNN as "fake news."

Police officers outside the Time Warner Centre where the CNN is based in New York, 25-10-2018. Image: Li Muzi/Xinhua News Agency/PA Images

After CNNs New York offices were evacuated for several hours yesterday, the network’s president Jeff Zucker said: "The president, and especially the White House press secretary, should understand that their words matter. Thus far they have shown no comprehension of that."

The package that arrived at CNN was addressed to John Brennan, a former director at the CIA.

He said: "Unfortunately, I think Donald Trump, too often, has helped to incite some of these feelings of anger, if not violence, when he points to acts of violence or also talks about swinging at somebody from the press, the media."

Meanwhile, Democratic leaders in Congress have warned that "time and time again, the president has condoned physical violence and divided Americans with his words and his actions."

New York mayor Bill de Blasio said: "This clearly is an act of terror attempting to undermine our free press and leaders of this country through acts of violence."

The devices were made from PVC pipe about six inches long and covered in black tape, X-ray images showed.

Investigators are now examining the explosive devices in the hope of finding forensic clues such as fingerprints and DNA which might enable them to identify the sender.