Investigators are expressing confidence they will identify who is responsible for sending 10 pipe bombs to prominent Democrats and critics of U.S. President Donald Trump.

"We will identify and arrest the person or people responsible for these acts," New York City Police Commissioner James O'Neill told reporters Thursday afternoon.

All the "suspected explosive devices" were being taken to the Federal Bureau of Investigation's laboratory at the U.S. Marine Corps base in Quantico, Virginia, said O'Neill.

"We are discovering things by the hour," he added at a news conference where other officials also said tips from the public were providing leads for investigators.

FBI Assistant Director William Sweeney, who is in charge of the bureau's New York field office, said "the investigation is still in its early stages," so he would not provide specific answers to the media about possible suspects or whether the pipe bombs were properly wired to explode.

Investigators are specifically looking at the southern part of the state of Florida as a source of some of the packages, according to media reports.

Trump is largely blaming the media for the angry political atmosphere in America that critics contend has led to what is being regarded as a wide-scale assassination attempt.

"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 said on Twitter on Thursday morning. (VOA)

• Emergency service personnel with a bomb-sniffing dog work outside the building that houses New York Governor Andrew Cuomo's office after a report of a suspicious package, Oct. 24, 2018, in New York.