iStock/Thinkstock(NEW YORK) — Former Vice President Joe Biden and actor Robert De Niro are the latest high-profile figures to be sent suspicious packages this week in a suspected mail-bomb campaign.

All of those to be sent the explosive devices and suspicious packages so far are prominent critics of President Donald Trump, but no motive has been determined for the mail-bomb campaign and no suspects have been identified.

A total of nine suspicious packages have been found as of Thursday in what has become a domestic terrorism investigation, law enforcement sources told ABC News. At least five contained devices resembling pipe bombs, intended to maim or kill.

Packages similar to those addressed to Biden and De Niro were sent to former Secretary of State Hillary Clinton, former President Barack Obama and CNN’s New York headquarters.

The package addressed to Biden was intercepted by law enforcement at a postal facility in New Castle, Delaware, sources told ABC News.

A package containing an explosive device sent to De Niro was discovered early Thursday morning in New York City’s Tribeca neighborhood, sources told ABC News. The device, similar to others recovered in the investigation, was removed by police in a bomb-containment vehicle.

Another package containing a device addressed to Democratic Rep. Maxine Waters of California was found in Los Angeles on Wednesday night. A prior one addressed to Waters was intercepted earlier Wednesday by Capitol Police in Washington, D.C.

A big concern among investigators Thursday morning was that there is a prolific bomb maker out there with the capacity to build more.

The FBI, Secret Service and the Bureau of Alcohol, Tobacco and Firearms (ATF) were fanning out across the country to determine where the items contained in the devices were purchased, which may give clues as to who is responsible.

X-ray photographs of the devices exclusively obtained by ABC News illustrate the critical leads investigators are now pursuing. Sources tell ABC News that each device contained a digital clock, explosive powder, a battery power source and wiring to channel a spark for detonation. The devices also included glass as potential shrapnel. The devices did not go off but had the potential to maim or kill.

The devices are also being examined for fingerprints and DNA. They were shipped in manila envelopes with America flag stamps.

Several of the packages had the return address of Democratic Rep. Debbie Wasserman Schultz of Florida, former chairperson of the Democratic National Committee. But her name was misspelled and Wasserman Schultz is not considered to be involved in sending the packages.

Several of the packages listed as a return address that of Rep. Debbie Wasserman Schultz, D-Fla., but her name was misspelled.

The deliveries of explosives come about two days after a pipe bomb was found in the New York home of billionaire George Soros, a Democratic supporter often criticized by right-wing groups.

“The FBI advises the public to remain vigilant and not touch, move or handle any suspicious or unknown packages,” the FBI said in a statement Wednesday evening. “We ask anyone who may have information to contact the FBI.”

The package addressed to Hillary Clinton was intercepted Tuesday night by the Secret Service at a screening facility. It didn’t reach her home in Westchester County.

All packages were intercepted before reaching their intended targets. It’s not entirely clear whether the incidents are linked, but authorities said they feared other bombs may have been sent.

Bryan Paarmann, special agent in charge of the FBI’s Counterterrorism Division and Joint Terrorism Task Force in New York City, said at a press conference on Wednesday that the mailings appear to be political in nature.

“The utilization of violence in order to further one’s own political agenda is unacceptable to us,” Paarmann said. “We will turn over every rock, we will turn every corner, and we will talk to everybody that we have to in order to mitigate this threat.”

President Trump on Wednesday night called for “peace and harmony” from a rally in Mosinee, Wisconsin, but added, “The media has a responsibility to set a civil tone and to stop the endless hostility and constant negative and oftentimes false attacks in stories.”

Also on Wednesday, from the White House, Trump said his administration is “extremely angry” about the incidents, adding that “the full weight of our government is being deployed to conduct this investigation and bring those responsible for these despicable acts to justice.”

Democratic leaders noted that most of the people targeted on Tuesday had been ridiculed by Trump.

“We listened with great interest to the president’s remarks this afternoon. We all take an oath to support and defend the Constitution and protect the American people, and that is our first responsibility. However, President Trump’s words ring hollow until he reverses his statements that condone acts of violence,” Rep. Nancy Pelosi, the House minority leader, and Sen. Chuck Schumer, the Senate minority leader, said in a joint statement released Wednesday afternoon. “Time and time again, the president has condoned physical violence and divided Americans with his words and his actions: expressing support for the Congressman who body-slammed a reporter, the neo-Nazis who killed a young woman in Charlottesville, his supporters at rallies who get violent with protesters, dictators around the world who murder their own citizens, and referring to the free press as the enemy of the people.”

Hillary Clinton, speaking at a campaign event in Florida, said, “We are fine, thanks to the men and women of the Secret Service who intercepted the package addressed to us long before it reached our home.”

“But it is a troubling time, isn’t it?” Clinton added. “And it’s a time of deep divisions, and we have to do everything we can to bring our country together.”

Security was tight at the event in Coral Gables where she spoke. Her daughter tweeted thanks to the Secret Service for not letting the package reach her mother.

“Every day, I am grateful to the women and men of the United States Secret Service,” Chelsea Clinton wrote. “Thank you.”

Her father also tweeted about it.

ABC News has confirmed the following:

— A pipe bomb was found Monday afternoon in the home mailbox of Soros in Westchester County north of New York City.

— A package addressed to Hillary Clinton containing an explosive was intercepted Tuesday night by the Secret Service at a screening facility. It never reached her home, where Bill Clinton was at the time.

— A package containing an explosive and suspicious powder was found Wednesday morning in the mailroom of the Time Warner Center in Manhattan, where CNN is located. It was addressed to John Brennan, former director of the CIA. New York City police officers were present when it was found.

— The package addressed to Holder did not reach its intended destination and was returned to Wasserman Schultz’s address in Florida, the FBI said.

— The devices found in New York, Washington and Florida were all similarly constructed, using digital clocks as a switch, a powder charge and a battery power source, law enforcement sources told ABC News. They were built using PVC pipe and contained materials likely intended to do additional harm.

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