Files found at a Libyan government building show strong cooperation between the CIA and Muammar Gaddafi's intelligence agencies, according to documents found after the fall of Tripoli to the Libyan rebels.

The Central Intelligence Agency, under the administration of then-president George W Bush, brought terror suspects to Libya and suggested questions that Libyan interrogators should ask them, the Wall Street Journal reported, citing documents found at the headquarters of Libya's External Security agency.

The files were uncovered by Human Rights Watch researchers who toured the Libyan government building, and gave copies to the WSJ.

The CIA also moved to set up in 2004 "a permanent presence" in the country, according to a note from CIA top operative Stephen Kappes to Libya's intelligence chief, at the time, Moussa Koussa.

Suggesting the close relationship between the two top clandestine services officials, the note begins "Dear Musa" and was signed "Steve," said the WSJ.

The documents were discovered Friday by journalists and Human Rights Watch. There were at least three binders of English-language documents, one marked CIA and the other two marked MI-6, among a larger stash of documents in Arabic.

An unnamed US official quoted by the daily noted that, at the time, Libya was breaking diplomatic ice with the West.

"Let's keep in mind the context here: By 2004, the US had successfully convinced the Libyan government to renounce its nuclear-weapons program and to help stop terrorists who were actively targeting Americans in the US and abroad," said the official.

The Americans sent terrorism suspects at least eight times for questioning in Libya despite that country's reputation for torture, the NYT reported, noting that the files left behind as Tripoli fell to rebels show that the cooperation was much more extensive than generally known with both the CIA and its British equivalent, MI-6.

Some documents indicate that the British agency was even willing to trace phone numbers for the Libyans, and another appears to be a proposed speech written by the Americans for Col. Muammar el-Gaddafi about renouncing unconventional weapons.

The documents cover 2002 to 2007, with many of them concentrated in late 2003 and 2004, when Moussa Koussa was head of the External Security Organization. (Mr Koussa was most recently Libya's foreign minister.