WASHINGTON — At least two more suspicious packages or devices were intercepted Thursday, addressed to prominent Democratic figures or supporters, as the investigation intensified into who sent them.

5:13 p.m.

According to the Associated Press, investigators are saying that their search of a mail database in the package bomb probe is leading them toward Florida.

4:08 p.m.

A former FBI agent in Tampa said he believes there will soon be an arrest in connection with the series of pipe bombs sent to Democratic politicians and CNN.

Retired FBI Agent Dave Couvertier says the person or persons responsible likely left behind a clue that could lead to an arrest. In the meantime, he recommends everyone remain on high alert. 

"Overall, just be cautious and just increase your vigilance," Couvertier said. "And anyone that knows anything about this particular situation should be contacting their local law agency or the FBI."

- Dave Jordan, Spectrum News

4:04 p.m.

An FBI official confirms some package bombs targeting President Donald Trump critics were sent through U.S. mail.

Meanwhile, a U.S. postal official says investigators looking for other package bombs have found nothing in the last 8 hours.

3:20 p.m.

The FBI is investigating whether the bombs were rigged to detonate, or were just meant to sow fear.

Two law enforcement officials with information about the investigation told the Associated Press the devices were not rigged to explode upon opening. There didn't appear to be any trip wire or ignition.

9:15 a.m.

The intercepted suspicious packages addressed to actor Robert De Niro and former Vice President Joe Biden are similar to those that contained crude pipe bombs sent to former President Barack Obama, former Secretary of State and Sen. Hillary Clinton and CNN offices in New York, investigators say.

A second package addressed to Biden was found at a Delaware postal facility that was also similar to the others containing crude bombs, the Associated Press reported.

8:39 a.m.

On Wednesday, President Donald Trump said about ths packages sent to Democratic figures and CNN, "Acts or threats of political violence have no place in the United States. This egregious conduct is abhorrent."

However, on Thursday, he tweeted the following:

Earlier in the week, Trump praised Republican Rep. Greg Gianforte for body-slamming a reporter during an election race last year. Gianforte pleaded guilty to that incident. 

8:20 a.m.

A package may have been sent to former Vice President Joe Biden, according to a law enforcement official, reported the Associated Press. The package is considered suspicious, but few details have been released. The package was misaddressed and returned to sender.

The FBI has confirmed that law enforcement officials were at a U.S. mail facility in New Castle, Delaware, but no further information has been released.

Earlier coverage

A senior law enforcement source has told Spectrum News that a suspicious device was found at an address associated with actor Robert De Niro in the TriBeCa section of New York on Thursday morning.

According to the New York City Police Department, the package was found near Greenwich and Franklin streets.

Another package was addressed to U.S. Rep. Maxine Waters, D-Calif., which was intercepted Wednesday night at a Los Angeles mail facility.

A law enforcement official said the package has similar characteristics to several others that were discovered this week.

Later on Thursday, a FBI spokesperson told CNN that the agency is responding to a U.S. postal facility in Delaware, but did not go into details.

Authorities think they've found a suspicious package addressed to Joe Biden, law enforcement officials said.

Suspicious packages appearing to be bombs targeted former first lady and U.S. Sen. Hillary Clinton, former President Barack Obama, U.S. Rep. Debbie Wasserman Schultz in South Florida and CNN's New York offices, among others.

Law enforcement says the bombs were packed with shards of glass. None of the packages reached their intended targets.

However, authorities warned they might not have found them all yet.

"We're working with the Postal Service to see if we can predict if any more of these packages do show up," said New York City Police Commissioner James O'Neill.

President Donald Trump condemned the attacks.

"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.

The targets of the bombs were some of the figures most frequently criticized by Trump, who still assails Clinton at rallies while supporters chant "lock her up" — two years after he defeated her and she largely left the political scene. Trump also often singles out cable news network CNN as he rails against the "fake news" media.

Law enforcement officials said all the packages were similar: manila envelopes with bubble-wrap interior bearing six stamps and the return address of 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 FBI said an additional package was intended for former Attorney General Eric Holder, but that one ended up at a Florida office of Wasserman Schultz, whose return address was on it.

The package intended for Holder had the wrong address and was forwarded to Wasserman Schultz.

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.

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.

None of the seven bombs (not including De Niro's package) detonated and nobody was hurt as authorities in New York, Washington, D.C., Florida and California seized the suspicious packages.

The devices all were sent to an FBI lab in Virginia to be studied. Officials provided no details on a possible suspect or motive.

The Associated Press contributed to this story.