Media reports Thursday said that Maher Arar, a 32-year-old Syrian-born telecommunications engineer, was deported by the INS after being detained at New York's John F. Kennedy Airport, where he had sought to return to Montreal after visiting his family in Tunisia.
The incident took place on Sept. 26.
It was not clear whether Arar had actually been charged with any offense by U.S. authorities.
U.S. officials refused to explain why he had been detained and deported, the Globe and Mail newspaper said. The newspaper quoted INS officials as saying that they had been ordered not to comment on the incident.
Canadian Foreign Affairs Minister Bill Graham said: "I have registered our protest to the United States. A person travelling on a Canadian passport is a Canadian citizen and has a right to be treated as a Canadian citizen."
Arar gained Canadian citizenship in 1987. He lived in Montreal and Ottawa and was well-known in the Canadian telecommunications industry. Married, with two children, he reportedly once worked for a Boston-area software firm.
The Canadian Broadcasting Corp. reported that U.S. authorities informed Canadian authorities only after the deportation and that high-level discussions between Ottawa and Washington were being held on the matter.
The CTV television network said that Amal Oummih, a New York immigration lawyer, tried to assist Arar while he was detained.
She said she had examined an INS document indicating that Arar had been detained "for allegedly being a member of a terrorist organization, to wit al Qaida."
She added that he may face severe punishment in Syria for having avoided conscription in that country.
U.S. Ambassador to Canada, Paul Cellucci, is also reported to have refused comment on the case, except to assert that U.S. officials had been justified in the deportation.
"All I can say is that the INS had good and sufficient reason for what they did, based on the current threat," Cellucci reportedly said.
News reports indicated that Arar may have been an acquaintance of one or more persons appearing on a list of suspected al Qaida members and was flagged for attention by immigration authorities following the events of Sept. 11.
Several such cases have sparked diplomatic friction between the United States and Canada in the recent past.