Contreras oversaw the much-feared security service DINA

The report adds that the contact was maintained until 1977 - a year after Contreras plotted the killing of the then Chilean Foreign Minister and foe of General Pinochet, Orlando Letelier, in Washington.

A BBC correspondent in Washington, Nick Bryant, says the documents reinforce the view that the US turned a blind eye towards political repression in Chile during the Pinochet era and that the CIA was complicit in many human rights abuses.

Pinochet's confidant

As head of the security service, DINA, Contreras became the one of the most feared men in Chile, second only to General Pinochet.

The general's iron rule was underpinned by the tactics of brutal repression that saw thousands die and thousands more flee into exile. Others disappeared or were tortured.

This report to Congress is the first step towards opening the door of the CIA's covered past in Chile, the first description of CIA ties to the organs of violent repression in Chile

Chile expert Peter Kornblush

Contreras, who was General Pinochet's closest friend and confidant in the five years after the military coup, was given a seven-year sentence in 1993 by a court in Chile for his role Mr Letelier's death.

The incident, in which a colleague of Mr Letelier also died, has been described as one of the worst cases of state-sponsored terrorism in the US.

Bloody coup

The report explains that the CIA maintained its relationship with Contreras because it viewed it as necessary to "accomplish the CIA's mission".

It says this was despite concerns that this relationship might lay the CIA open to charges of aiding internal political repression.

Contreras masterminded the murder of Pinochet foe Orlando Letelier

The documents add that the CIA, despite warning Contreras about committing human rights abuses, made a one-off payment to him in 1975.

"The CIA says the payment was a mistake, but I don't see them saying that they took the payment back or that they told Contreras that they didn't want anything to do with him," said Peter Kornblush, Chile expert at the non-governmental National Security Archive.

"Quite the contrary - they continued to work with him."

The report denies that the CIA was involved in bringing General Pinochet to power in a bloody coup.

At least 5,000 were killed in the September military onslaught, among them the democratically-elected President Salvador Allende.

Previous documentary evidence indicates that the administration of former US President Richard Nixon was involved in efforts in the early 1970s to overthrow the socialist President Allende, or to prevent him from taking office.

It also maintained close ties to the Chilean secret police.