New York police have recovered a suspicious package addressed to actor Robert De Niro which may contain a device similar to others sent to leading Democrats, officials said.
Security personnel at Tribeca Productions summoned police at around 5am on Thursday and the bomb squad removed the package and took it away for investigation. Police said it appears to be from the same sender.
The Hollywood star has been an outspoken critic of US president Donald Trump.
A package addressed to former vice president Joe Biden is also being investigated after it was intercepted at a Delaware mail centre. Police said the item found in New Castle appeared similar to other packages containing bombs.
The discovery came after a series of glass-filled pipe bombs targeting Hillary Clinton, former president Barack Obama, other prominent Democrats and CNN were thwarted without injury.
None of the bombs detonated as law enforcement took them away for examination and disposal.
The first crude bomb to be discovered had been delivered on Monday to the New York compound of George Soros, a liberal billionaire and major contributor to Democratic causes.
The FBI said an additional package was intended for former Attorney General Eric Holder, but that one ended up at a Florida office of Democratic representative Debbie Wasserman Schultz, whose return address was on it.
Later on Wednesday, the FBI said two additional packages addressed for Democrat representative Maxine Waters had been intercepted that were similar in appearance to five others.
The targets of the bombs were some of the figures most frequently criticised by Mr Trump.
He accuses Mr Soros of paying protesters and singles out cable news network CNN as he rails against the “fake news” media.
The attacks overtook other news in an already-tense political season that could reshape Congress and serve as a referendum on the first two years of Mr Trump's presidency.
The actions, which caused panicked building evacuations and reports of additional explosives that later proved unfounded, are bound to add to fears that overheated rhetoric could lead to deadly violence as the parties engage in bitter fights over immigration, the US supreme court and the treatment of women.
The White House condemned the attacks aimed at Democrats and other perceived foes of the administration.
"Acts or threats of political violence have no place in the United States, " Mr Trump said. "This egregious conduct is abhorrent."
Other Republican leaders said the same.
But Democratic Senate and House leaders Chuck Schumer of New York and Nancy Pelosi of California said such words "ring hollow" when coming from Mr Trump.
Law enforcement officials said all the packages were similar: manila envelopes with bubble-wrap interior bearing six stamps and the return address of Florida representative Schultz.
She is the former chairwoman of the Democratic National Committee who was accused by Clinton rivals of secretly helping the party's eventual presidential nominee.
The pipe bombs were packed with powder and shards of glass. The devices, each with a small battery, were made from PVC pipe about six inches long and covered with black tape, said a law enforcement official who viewed X-ray images.
The devices all were sent to an FBI lab in Virginia to be studied. Officials provided no details on a possible suspect or motive.
"Suffice it to say, it appears an individual or individuals sent out multiple, similar packages," said John Miller, the New York Police Department's head of intelligence and counter-terrorism.
The US secret service intercepted a bomb that was addressed to Hillary Clinton at the New York home she shares with former president Bill Clinton, and another that was sent to Mr Obama at his home in Washington.
A police bomb squad removed still another from CNN's New York office, which was evacuated. The CNN package was addressed to former CIA director John Brennan, who has publicly clashed with Mr Trump and is a regular television contributor.
Speaking at an event in Austin, Texas, Mr Brennan called the spate of pipe bombs “an unfortunate turn of events”.
“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,” he said.
The package sent to CNN contained a live explosive, with wires and a black pipe, and an envelope with white powder, officials said.
The powder was tested and determined to have been harmless, according to a law enforcement official.
New York City Police Commissioner James O'Neill says investigators are reviewing security video to see if they can identify a courier believed to have delivered the pipe bomb package to CNN's office.
Mr O’Neill said in an appearance on CNN that he was “pretty sure those images will be caught on video and we’ll be able to find out where that person came from before they entered the building and where they went to after”.
New York governor Andrew Cuomo said his office received a similar package, but New York police officials said the office was cleared and no device was found.
Neither Mrs Clinton nor Mr Obama received the packages sent to them, and neither was at risk because of screening procedures, the Secret Service said.
White House press secretary Sarah Sanders said in a statement: "These terrorising acts are despicable, and anyone responsible will be held accountable to the fullest extent of the law." – AP