Federal agents have searched a mail facility near Miami as they race to find who sent 10 pipe bombs to prominent Democrats and critics of Donald Trump, as the president on Friday accused the media of blaming him for the unfolding of what is believed to be domestic terrorism.

The homeland security secretary, Kirstjen Nielsen, told Fox News: “Some of the packages went through the mail. They originated, some of them, from Florida. I am confident that this person or people will be brought to justice.”

On Thursday, the FBI was also examining devices sent to the former US vice-president Joe Biden and the actor Robert De Niro. Two packages for Biden were intercepted in Delaware, according to the FBI, while another was received at De Niro’s offices in New York. Investigators said they matched those sent to Barack Obama and several other Democrats this week, which contained pipe bombs. One was also sent to the offices of CNN in New York, which caused the building to be evacuated and journalists to broadcast live from the street outside instead.

Play Video 2:17 'Words matter': Joe Biden speaks out hours after being targeted with pipe bomb – video

The new discoveries mean eight high-profile Trump critics have been sent a total of 10 packages. All were intercepted and removed without detonating, and no injuries were reported.

On Friday morning, the president tweeted: “Funny how lowly rated CNN, and others, can criticize me at will, even blaming me for the current spate of Bombs.”

A police bomb squad and canine units joined federal investigators examining a mail distribution center at Opa-locka, north-west of Miami, on Thursday, said Miami-Dade county police. The sprawling warehouse, where authorities believe several of the parcels were processed, appeared to remain in operation during the search.

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The New York police commissioner, Jim O’Neill, said at a news conference on Thursday afternoon that investigators were also following up tips from the public. “We are discovering things by the hour,” he said.

Officials said people thought to be at risk of receiving the devices had been identified, warned and given help screening their mail. John Miller, the New York police department’s deputy commissioner for intelligence and counter-terrorism, said of the packages: “We’re watching where they go.”

Those targeted so far appeared to share a record of clashing with Trump and becoming figures of loathing among some of his supporters.

Biden has stridently condemned Trump’s presidency since leaving office, while De Niro received a standing ovation at the Tony awards in New York in June for a speech criticising the president. A spokesman for Biden declined to comment.

Trump and White House officials on Thursday rejected suggestions that he bore any responsibility for the circumstances around the attempted bombings, instead claiming that the media was to blame for the US’s inflamed politics.

“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,” Trump tweeted. “It has gotten so bad and hateful that it is beyond description. Mainstream Media must clean up its act, FAST!”

And on Friday morning the president followed up with a tweet railing against the media’s role in criticizing him and accusing cable news channel CNN of exaggerating the severity of the latest terrorist campaign of explosive packages.

Donald J. Trump (@realDonaldTrump) Funny how lowly rated CNN, and others, can criticize me at will, even blaming me for the current spate of Bombs and ridiculously comparing this to September 11th and the Oklahoma City bombing, yet when I criticize them they go wild and scream, “it’s just not Presidential!”

One of the suspect packages, which police said contained a “live explosive device”, was sent to the New York studios of CNN, one of the most frequent targets of Trump’s campaign to discredit the media. The channel’s journalists were evacuated.

Facebook Twitter Pinterest Police outside the Time Warner Center in New York, which houses the CNN headquarters, after it was evacuated due to a suspicious package. Photograph: UPI/Barcroft Images

Speaking at an event in Washington on Thursday, Trump’s attorney general, Jeff Sessions, said FBI agents were working around the clock to find the person or people responsible for the bombs.

“Across this administration – across this country – we condemn these actions in the strongest possible terms and we are determined that justice will be done,” said Sessions.

In addition to Obama, his former secretary of state Hillary Clinton, the former CIA director John Brennan and the former attorney general Eric Holder were all sent packages containing pipe bombs, according to US authorities. Brennan’s was sent to CNN, where he has appeared as a commentator after leaving the government.

Congresswoman Maxine Waters of California was sent two packages and George Soros, a wealthy donor to liberal causes, received one in the mailbox of his New York home. Both are frequently derided by Trump and his Republican allies.

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The packages were being analysed by the FBI at its laboratory in Quantico, Virginia.

X-ray photographs leaked to the media suggested that at least some of the packages contained pipes packed with explosive powder along with shrapnel such as pieces of glass. Andrew Cuomo, the governor of New York, said on Thursday that the devices were viable bombs.

Facebook Twitter Pinterest The scene outside the New York offices of Robert De Niro, where a package was also sent. Photograph: Vanessa Carvalho/Rex/Shutterstock

Bombs sent, people threatened … Trump's response? Attack the media Read more

Charles Schumer and Nancy Pelosi, the Democratic leaders in Congress, said Trump’s condemnations of the attempted bombings rang hollow while he continued making remarks such as his praise for a congressman who physically assaulted a Guardian reporter last year.

“Time and time again, the president has condoned physical violence and divided Americans with his words and his actions,” they said in a joint statement, as the midterm elections approach on 6 November.

But Sarah Sanders, the White House press secretary, told reporters: “The president is certainly not responsible for sending suspicious packages, any more than Bernie Sanders was for a supporter shooting up a baseball practice.”

In June last year, James Hodgkinson, a former volunteer for Bernie Sanders’ campaign for the Democratic presidential nomination, opened fire on Republican congressmen at a baseball training session in Virginia, seriously wounding Steve Scalise of Louisiana.

Play Video 1:36 Donald Trump vows US will 'get to the bottom' of pipe bombs - video

Trump condemned the attempted bombings on Wednesday and said unity was needed in the US. But within hours at a campaign rally he was attacking the media for negative coverage.