The government memos were released this week under Canada's Access to Information Act. The Associated Press obtained them Thursday from The Canadian Press.

Internal government briefing notes revealed senior intelligence officials from six government agencies, including the Security Intelligence Service, met in late November to discuss the flights.

One memo dated Nov. 28 instructed officials to tell the media that there was ``no credible information to suggest that these planes were used to ferry suspected terrorists to and from Canada, or that illegal activity took place.''

A spokesman for the CIA in Washington declined comment on Thursday.

U.S. intelligence officials have said in the past that the planes are more likely to be carrying staff, supplies or Director Porter Goss on his way to a foreign visit.

The U.S. has come under fire, especially in Europe, for the practice of ``extraordinary rendition'' - the transporting of terror suspects to countries where they face harsh interrogation methods and possibly torture.

Ottawa has been investigating the detention of Syrian-born Canadian engineer Maher Arar. He was detained at JFK International Airport in New York in September 2002 on suspicion of being a member of Osama bin-Laden's al-Qaida network.

U.S. authorities deported Arar to Syria, where he was kept in a damp Damascus prison cell and allegedly tortured for 10 months before being released and flown back to Canada.

Last November, journalists and the Opposition in Parliament - the Conservative Party that now is in power - raised allegations that at least six aircraft linked to alleged front companies for the CIA had landed at Canadian airports in the previous six months.

One of the briefing notes, which is stamped ``SECRET,'' said that Canada Border Services Agency reported that 20 aircraft had made 74 flights to Canada since the 9/11 terrorist attacks on New York and Washington.

After the attacks on the World Trade Center and the Pentagon, President Bush gave the CIA authority to conduct the operations and permitted the agency to act without case-by-case approval from the White House or other administration offices.

U.S. government officials say the operations are used for those considered by the CIA to be the most serious terror suspects.

The European Union has demanded answers from the State Department about reports of secret U.S.-run prisons for terrorism suspects in Europe.

Romania, meanwhile, challenged human rights groups Thursday to provide evidence that his country hosted a secret U.S. detention center or allowed its airports to be used in CIA transfers.

The New York-based Human Rights Watch organization has alleged terror suspects captured in Afghanistan have been transported through Romania, which has denied the claims.

Romanian Foreign Minister Mihai Razvan Ungureanu, who was in London for talks, said there remained no proof of impropriety.

``I've always asked those who pretend to have proof, to offer us that proof, it would be extremely important for us,'' Ungureanu told a news conference.

The Public Safety Department in Ottawa said in January that a federal review of landings by the supposed CIA flights showed no evidence of ``illegal activities.''

Amnesty International said the Canadian government has yet to provide the human rights group evidence that the flights were not used to ferry terror suspects to foreign prisons.

``There's clearly a range of international human rights concerns associated with flights of this description,'' said Alex Neve, secretary general of Amnesty's Canadian arm.

He said Ottawa should be held responsible if it is determined that the flights did in fact deliver terror suspects into torture, a violation of the Canadian constitution.

``If you're part of the chain of events that make that happen, then your human rights responsibility as a government are engaged,'' Neve said.

Flight data obtained by The Canadian Press show that since mid-2005, at least seven different planes owned by reputed CIA shell corporations have landed at Canadian airports.

One recent flight, an 11-seat Beech turboprop, set out for Keflavik, Iceland, on Feb. 12 from Goose Bay, Newfoundland and Labrador, where it had arrived the previous day from Montreal.

The U.S. military maintains an air station in Keflavik, which serves as a refueling point for Europe-bound aircraft.