President Donald Trump called on the media “to stop the endless hostility”, after a series of suspected explosives were posted to high-profile US figures and media.
US authorities are investigating after glass-filled pipe bombs were sent to addresses including the offices of CNN in New York.
Two other suspicious packages were sent to President Barack Obama and former Democratic presidential candidate Hillary Clinton.
Speaking at a rally on Wednesday, Trump vowed to catch the perpetrator as he called for an end to attacks on political figures.
“Those engaged in the political arena must stop treating political opponents as being morally defective.
“No one should carelessly compare political opponents to historic villains, which is done often.”
He called on the media to end “constant negative and oftentimes false attacks and stories”.
The targets of the bombs were some of the figures most frequently criticised by the US president.
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 Representative Debbie Wasserman Schultz, whose return address was on it.
Two additional packages similar to the others were addressed to Democrat Representative Maxine Waters but intercepted, the intelligence service said.
Earlier, CNN president Jeff Zucker criticised the administration for a “total and complete lack of understanding at the White House about the seriousness of their continued attacks on the media,” he said.
The Time Warner building was evacuated on Wednesday morning after reports of a suspicious package which police later said they believed was a pipe bomb.
The New York Police Department’s bomb squad said the situation was now under control, and there are no reports of any injuries.
The 24-hour rolling news channel cut to commercials after its live broadcast was interrupted by an alarm.
It is not yet known if the CNN incident is linked to the other devices.
The package to Clinton was found late on Tuesday while the one addressed to Obama was found early on Wednesday, both during routine mail screenings, the US Secret Service (USSS) said.
Both were identified as “potential explosive devices and appropriately handled as such”.
Assistant Special Agent Mason Brayman added: “The protectees [Clinton and Obama] did not receive the packages nor were they at risk of receiving them.
“The Secret Service has initiated a full scope criminal investigation that will leverage all available federal, state, and local resources to determine the source of the packages and identify those responsible.”
The FBI’s New York Office is also investigating.
White House spokeswoman Sarah Huckabee Sanders said: “These terrorising acts are despicable, and anyone responsible will be held accountable to the fullest extent of the law.”
She continued: “The United States Secret Service and other law enforcement agencies are investigating and will take all appropriate actions to protect anyone threatened by these cowards.”
The suspicious packages sent to the two top Democrats as well as a bomb sent to one of their major donors came roughly two weeks ahead of the high-stakes November 6 election that will determine whether Republicans maintain control of Congress in a nation that has become deeply polarised.
Officials said the devices are similar to those sent to the home of billionaire financier George Soros on Monday.
Investigators have not named any suspects or disclosed a possible motive, but Soros has become a hated figure among some right-wing activists in the United States and Eastern Europe, and the target of a hostile media campaign by the nationalist government in his native Hungary.