The head of the U.S. Senate Intelligence Committee has publicly accused the CIA of improperly accessing computers used by congressional staff, BBC News reports.

Senator Dianne Feinstein said on the Senate floor that such activities "may have undermined the constitutional framework" of government oversight.

The Senate committee was investigating allegations of abuse during a CIA detention and interrogation program.

A CIA internal watchdog has been tasked with looking into the alleged hacking.

"I am not taking it lightly," Feinstein said of the matter on Tuesday, March 11, adding that the CIA may have violated federal laws in its alleged conduct.

The agency is accused of secretly removing documents from computers used by the Senate Intelligence Committee during an investigation into alleged CIA abuse.

That alleged abuse is said to have stemmed from a detention and interrogation program under former President George W Bush.

Feinstein has told U.S. media in the past that the committee's 6,000-page "comprehensive review", completed in 2013, found the CIA program 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".

CIA inspector general David Buckley has been tasked with looking into the alleged actions, but CIA director John Brennan rejected the Senate allegations last week.

"I am deeply dismayed that some members of the Senate have decided to make spurious allegations about CIA actions that are wholly unsupported by the facts," he said on March 5. "I am very confident that the appropriate authorities reviewing this matter will determine where wrongdoing, if any, occurred in either the Executive Branch or Legislative Branch."