The package sent to De Niro was discovered at an address associated with the actor around 5 a.m. near Greenwich and Franklin streets. Tribeca area of New York City. The Tribeca Grill, owned by De Niro, is also located there.
Police decided to move the package to the NYPD's facility at Rodmans Neck in the Bronx for further investigation.
The NYPD moved the package in their total containment vessel, otherwise known as their bomb truck.
In addition to the package sent to De Niro, authorities are also investigating a suspicious device addressed to former Vice President Joe Biden that was recovered at a postal facility in Wilmington, Delaware Thursday morning.
Investigators said they were similar to crude pipe bombs sent to former President Barack Obama, Hillary Clinton and CNN. None of the bombs have detonated and no one was hurt as authorities in New York, Washington, D.C., Florida and California seized the suspicious packages.
The targets of the bombs were some of the figures most frequently criticized Trump, who still assails Clinton at rallies while supporters chant "lock her up" - two years after he defeated her. Trump also often singles out cable news network CNN and other news media whose reporting he does not like, terming them "fake news."
On Thursday, without directly referencing the explosive devices, Trump again blamed the media for the "anger" in society.
"A very big part of the Anger we see today in our society is caused by the purposely false and inaccurate reporting of the Mainstream Media that I refer to as Fake News," he said in a morning Tweet. "It has gotten so bad and hateful that it is beyond description. Mainstream Media must clean up its act, FAST!"
TIMELINE: Multiple suspicious packages sent to Clintons, Obamas, CNN, Robert De Niro and others
Hours earlier, he took a softer tone at a rally in Wisconsin Wednesday night.
"Let's get along," he said. "By the way, do you see how nice I'm behaving tonight? Have you ever seen this?"
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 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 Supreme Court and the treatment of women.
The bombs, each with a small battery, were about six inches long and packed with powder and broken glass, said a law enforcement official who viewed X-ray images and spoke on condition of anonymity to discuss an ongoing investigation.
The official said the devices were made from PVC pipe and covered with black tape.
The first crude bomb to be discovered had been delivered Monday to the suburban 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 Rep. Debbie Wasserman Schultz, whose return address was on it.
Later Wednesday, the FBI said two additional packages addressed for Rep. Maxine Waters had been intercepted that were similar in appearance to five others.
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," 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 Trump. They noted the president's recent praise of a GOP congressman who body-slammed a reporter, among other Trump statements.
Law enforcement officials said all the packages were similar: manila envelopes with bubble-wrap interior bearing six stamps and the return address of Florida Rep. Debbie Wasserman 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 package intended for Holder had the wrong address and was forwarded to Wasserman Schultz.
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 counterterrorism, who briefed reporters.
The U.S. Secret Service intercepted the bomb that was addressed to Hillary Clinton at the Chappaqua, New York, home she shares with former President Bill Clinton, and another that was sent to 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 Trump and is a regular television contributor.
Speaking at an event in Austin, Texas, Brennan called the spate of pipe bombs "a very unfortunate turn of events," particularly if he and others are being targeted for their public comments.
"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," Brennan 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 who spoke on condition of anonymity to discuss an ongoing investigation.
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. 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."
Waters, whom the president has denigrated as a "low-IQ individual," reported Wednesday afternoon that she was the target of a suspicious package. Though the FBI did not initially include her on a list of targeted individuals, the bureau later said two packages addressed to her and similar to the five others had been found. One was intercepted at a Los Angeles mail facility.
White House press secretary Sarah Sanders said in a statement, "These terrorizing acts are despicable, and anyone responsible will be held accountable to the fullest extent of the law."
But while stopping short of blaming Trump's rhetoric for inspiring the attacks, Jeff Zucker, the president of CNN Worldwide, contended there was a "total and complete lack of understanding at the White House about the seriousness of their continued attacks on the media."
"The president, and especially the White House press secretary, should understand their words matter. Thus far, they have shown no comprehension of that," he said.
All federal buildings including the Dirksen Building have heightened security. It's a precaution, because Chicago police said there were *no* threats anywhere in the city.
ABC News and WABC-TV and WLS-TV contributed to this report.