11 March 2014 Last updated at 16:29Senate intelligence committee chairwoman Senator Dianne Feinstein said the alleged CIA conduct could have violated federal laws
The head of the US Senate intelligence committee has publicly accused the CIA of improperly accessing computers used by congressional staff.
Senator Dianne Feinstein said on the Senate floor that such activities "may have undermined the constitutional framework" of government oversight.
The Senate panel was investigating allegations of abuse during a CIA detention and interrogation programme.
A CIA internal watchdog has been tasked with looking into the alleged hacking.
"I am not taking it lightly," Ms Feinstein said of the matter on Tuesday, adding that the CIA may have violated federal laws in its alleged conduct.
But CIA director John Brennan rejected the Senate allegations.
"The CIA was in no way spying... on the Senate," he told MSNBC on Tuesday.
The agency is accused of secretly removing documents from computers used by the Senate intelligence committee during an investigation into alleged CIA abuse.
Those computers were provided by the CIA to congressional members of staff at a secure site so that Senate investigators could review millions of pages of top secret documents.
The alleged CIA abuse stemmed from a detention and interrogation programme under former President George W Bush.
Ms Feinstein has previously said that the committee's 6,000-page "comprehensive review" - completed in 2013 and encompassing six million pages of records - found that the CIA programme had yielded little or no significant intelligence.
On Tuesday, the Senate intelligence committee chairwoman reportedly said such improper access to congressional networks, if true, amounted to attempted intimidation of investigators.
She also said she had requested an apology from the agency and an acknowledgment that the search was inappropriate, but had "received neither" despite sending letters to the agency requesting information on 17 and 23 January.
Ms Feinstein noted that CIA inspector general David Buckley had been tasked with looking into the alleged actions.
She said he had already referred the matter to the Department of Justice, "given the possibility of a criminal violation by CIA personnel".