WASHINGTON (REUTERS, AFP) - US federal investigators are trying to track down suspicious packages, one of which was believed to be addressed to Mr Joe Biden, a federal official said on Wednesday (Oct 25), as the former Vice-President becomes the latest target of suspected package bombs sent to high-profile Democrats and CNN in what officials branded an act of terrorism.

Two more suspicious packages, similar to those intercepted before reaching US President Barack Obama and other Democrats, were found addressed to California Congresswoman Maxine Waters, the FBI said on Wednesday.

The two parcels intended for Waters, a veteran Democratic US representative from Los Angeles and an outspoken critic of Republican President Donald Trump, take to eight the total number of suspected package bombs under investigation.

None of the devices went off and no injuries were reported, but a number of top Democrats were quick to label the threats a symptom of a coarsening brand of political rhetoric promoted by President Donald Trump, who also condemned the acts.

"For years now, Donald Trump has been calling for the jailing of his critics and has lauded violence against journalists," said US Representative Bill Pascrell, a New Jersey Democrat.

"The danger of right-wing extremism cannot be ignored and more attention must be paid to it before even worse violence occurs."

Police intercepted six suspected bombs sent to targets including Mr Trump's 2016 presidential rival Mrs Hillary Clinton, former president Barack Obama, prominent political donor George Soros and news network CNN. Law enforcement agencies were investigating.

CNN is known for its robust coverage of the Trump administration and for constantly provoking the ire of the president. Signs at his rallies condemn the network.

Mr Trump on Wednesday called on the media to stop its "endless hostility" and "false attacks" in comments addressing the incident.

"No one should carelessly compare political opponents to historical villains, which is done, it's done all the time," he said at a campaign rally in Mosinee, Wisconsin.

"The media also has a responsibility to set a civil tone and stop the endless hostility and constant negative and oftentimes false attacks and stories," he added. "Have to do it. They've got to stop."

During his presidential campaign, Mr Trump regularly urged his supporters to chant "Lock her up", a threat to jail Mrs Clinton, and also supported conspiracy theories that Mr Soros plays an underhanded role in influencing US politics.

Politicians from both major parties have made condemning the harsh tone of politics part of their everyday stump speeches.

Republicans have criticised Democrats and liberal activists as a "mob", decrying protesters crowding the US Capitol to oppose Mr Trump's Supreme Court nominee Mr Brett Kavanaugh, and confronting and chastising Republican lawmakers in restaurants and other settings.

Scenes of small-scale violence also marked Mr Trump's 2017 inauguration.

A recent Reuters/Ipsos poll found rising anger would be a factor driving voters on the Nov 6 elections when Democrats are seeking to regain control of at least one of the two chambers of Congress.

Republicans, including Mr Trump, condemned the failed attacks.

"Acts or threats of political violence of any kind have no place in the United States of America," Mr Trump said at the White House. "We're extremely angry, upset, unhappy about what we witnessed this morning and we will get to the bottom of it."

Senate Democratic leader Chuck Schumer and House Democratic leader Nancy Pelosi dismissed Mr Trump's words, saying in a statement that they "ring hollow".

"Time and time again, the President has condoned physical violence and divided Americans with his words and his actions," the statement said.

HEATED TONE

Mr Trump sometimes invokes images of violence in remarks to his supporters. Last week, he reiterated his support for a Montana congressman who body-slammed a reporter in 2017. In August, Mr Trump warned that if Democrats gained control of Congress, they would "quickly and violently" overturn his agenda.

Last year, he said there were bad people on both sides of a clash in Charlottesville, Virginia, between white supremacist groups and counter-protesters.

Some of the people who received suspicious packages, including Mr Obama, Mrs Clinton and former attorney-general Eric Holder, have been targeted by online groups such as QAnon that push vast conspiracy theories saying Democrats are behind international crime rings.

Posts on online message boards dismissed the cluster of suspected bombs as a "false flag", an allegation that a widely covered news event was a politically motivated hoax.

Professor Paul Achter, a professor of rhetoric at the University of Richmond, said Mr Trump's frequently violent tone increased the likelihood of violent actions.

"Verbal abuse has consequences," Prof Achter said. "Just because Trump did not send a bomb or beat up a reporter or shoot up a newsroom doesn't excuse this kind of speech."

Last week, an association representing White House correspondents accused Mr Trump of "cheerleading" violence against the media after the president applauded an assault by a congressman on a reporter.

"There is a total and complete lack of understanding at the White House about the seriousness of their continued attacks on the media," said CNN president Jeff Zucker earlier on Wednesday.

"Words matter. Thus far, they have shown no comprehension of that."