OTTAWA -- The RCMP and Canadian Security Intelligence Service exchanged a considerable amount of information about Maher Arar, but it is unclear whether CSIS directly sent material to U.S. authorities, an official familiar with the high-profile case said Monday.

The revelation of information-sharing between Canada's two primary counter-terrorism agencies in the Arar matter raises new questions about intelligence possibly supplied to the U.S. in the increasingly muddled affair.

Arar, a Syrian-born Canadian citizen, was detained in New York on suspicions of terrorism in late September 2002.

The Ottawa telecommunications engineer, travelling on a Canadian passport, was subsequently deported by U.S. authorities to Syria, where he was tortured for months before being released. He denies any involvement in terrorism.

Separate watchdogs overseeing the RCMP and CSIS are probing the actions of the respective security agencies in the Arar matter.

The Security Intelligence Review Committee, which keeps an eye on CSIS, said Monday it was conducting an "in-depth review'' of the spy agency's involvement.

The Commission for Public Complaints Against the RCMP is delving into the Mounties' role in the Arar affair.

Officials who questioned Arar in New York last year possessed a copy of an Ottawa rental agreement he had signed in 1997, and Canadian authorities have not explained how the private document ended up in U.S. hands.

The comments of the official, who asked not to be named, indicate that if the RCMP supplied information on Arar to U.S. authorities, it may well have included material originally gleaned from CSIS, given the exchanges between the Mounties and the spy agency.

Without a thorough check, it is difficult to be certain if CSIS sent intelligence directly to the U.S. because Canadian and American security agencies routinely share information extensively, the official added.

"There's just enormous amounts of it going back and forth all the time.''

The intelligence review committee said it will examine "the nature and extent'' of any exchanges of information between CSIS and the RCMP, Foreign Affairs and intelligence agencies abroad.

CSIS has consistently said it had no role in the arrest or deportation of Arar. But the spy service has stopped short of addressing the question of whether information about him was shared with U.S. authorities.

Susan Pollak, executive director of the review committee, said the watchdog would examine ``the entire scope of CSIS's involvement'' in Arar's case.

"It's shocking to a lot of Canadians to see a Canadian citizen receive the kind of treatment he did,'' said Pollak.

"We need to know why this happened to this individual, how it could have happened. And I'm sure people want to feel that they are not going to be the next ones.''

The review committee's report will be submitted to Public Safety Minister Anne McLellan, likely in late spring of next year. An unclassified version, stripped of sensitive details, is to be made public.

Critics including Arar have called for a full public inquiry into the case to ensure all relevant facts emerge.