Senate Intelligence Committee Chair Dianne Feinstein (D-Calif.) said during a stunning speech the Senate floor Tuesday morning that the Central Intelligence Agency may have broken the law and violated the Constitution by searching a stand-alone computer network established for Congress.

Feinstein accused the CIA of searching the congressional network in January, during the Senate Intelligence Committee's ongoing investigation into the agency's detention and interrogation programs under President George W. Bush.

Feinstein said the matter has been referred to the Department of Justice for possible criminal prosecution.

"I have grave concerns that the CIA search may well have violated the separation of powers principles," Feinstein said. She added that she was "not taking it lightly," insinuating it was an attempt at intimidation.

The CIA provided Congress with the computers as part of the investigation so the committee could review classified documents at CIA headquarters. Each side has accused the other of spying. But the incident in question arose in December, when Intelligence Committee investigators got ahold of an internal agency review casting a particularly bad light on the interrogation and detention programs, which were ended by President Barack Obama.

CIA officials then searched the computers to try to determine how the committee investigators had gained access to the information, Feinstein said. She added that the committee did nothing improper to gain access to the internal reports.

"The CIA just went and searched the committee's computers," Feinstein said, breathlessly.

Later on Tuesday, CIA Director John Brennan disputed the allegations, saying "nothing could be further from the truth."

"That's just beyond the scope of reason," Brennan said during an event at the Council on Foreign Relations.

After Feinstein's speech, Vermont Sen. Pat Leahy called it historic and said he couldn't think of a more important one in Senate history.. Senate Majority Leader Harry Reid commended her for outlining "one of the most important principles we must maintain — separation of powers."

Feinstein opened the Senate's Tuesday session after an all-night session during which 30 Democratic senators waged a "talk-a-thon" on the topic of climate change. She repeatedly said she was speaking "reluctantly," because of inaccurate press reports over the past few weeks.

Feinstein spoke for more than 40 minutes.

Here is Feinstein's full statement: