Washington(CNN) President Donald Trump returned on Thursday to blaming the media for much of the "anger" in society, a day after CNN and Democrats were the targets of explosive devices.

"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!" he continued.

Although the President has often derided the media as "fake news," even labeling reporters the "enemy of the people," Thursday's tweet is especially striking in the wake of potential attacks on a major media outlet and political figures who have criticized him.

Former CIA Director John Brennan, who was an intended recipient of one of the packages, responded to Trump's tweet, telling the President to "stop blaming others" and "look in the mirror."

"Your inflammatory rhetoric, insults, lies, (and) encouragement of physical violence are disgraceful," Brennan wrote on Twitter to the President. "Clean up your act....try to act Presidential. The American people deserve much better."

He added that the President's "critics will not be intimidated into silence."

Republican Sen. Ben Sasse of Nebraska argued that "we need to stop with all this nonsense language about the press is the enemy of the people."

"Every American needs to be against political terrorism. And so that starts at the top that the President has the biggest bully pulpit in America, and he needs to affirm again that we condemn all political terrorism in America," Sasse said in an interview on CNN.

White House press secretary Sarah Sanders defended Trump's comments on the media while taking questions from reporters Thursday, saying he has "condemned violence in all forms, has done that since Day 1."

She deflected when asked whether the President bears any responsibility for the heated political rhetoric.

"The President is certainly not responsible for sending suspicious packages to someone," Sanders told reporters. "No more than Bernie Sanders was responsible for a supporter of his shooting up a Republican baseball field practice."

In 2017, a gunman opened fire on a Republicans' congressional baseball practice in Virginia.

As Trump was tweeting, New York authorities were removing a suspicious package addressed to actor -- and frequent Trump critic -- Robert De Niro at a building in Lower Manhattan's Tribeca neighborhood. The package has markings similar to the pipe bomb packages recently mailed nationwide to top Democrats, two law enforcement sources said.

In the initial aftermath of the bomb discoveries Wednesday, Trump offered a more conventional presidential message of unity, condemning the attack and calling on Americans to "unify" and "come together and send one very clear, strong, unmistakable message that threats or acts of political violence have no place in the United States of America."

Trump also began an evening rally in Wisconsin by voicing his desire for "all sides to come together in peace and harmony."

But he also pointed the finger at the media, saying that the press has a "responsibility" to foster civility.

"The media also has a responsibility to set a civil tone and to stop the endless hostility and constant negative and oftentimes false attacks and stories. Have to do it," he said at the rally.

A federal investigation has launched into who is behind the packages containing pipe bombs sent to several prominent Democrats across the country. On Wednesday, the US Secret Service announced that it had intercepted explosive devices mailed to former President Barack Obama in Washington and 2016 Democratic nominee Hillary Clinton in New York, following the discovery of an explosive device at the New York home of Democratic donor George Soros.

Later in the day, CNN's New York bureau was evacuated after a pipe bomb was discovered in a package addressed to Brennan.

The day continued with more suspicious packages discovered by law enforcement intended for California Democratic Rep. Maxine Waters and former attorney general Eric Holder.

Law enforcement officials said Thursday they tracked down another suspicious package sent to former Vice President Joe Biden.