The chief White House envoy to Ottawa says the United States can't guarantee other Canadians won't face the same fate as Maher Arar.

Speaking to reporters after a conference on Canada-U.S. relations in Ottawa on Thursday, American ambassador Paul Cellucci said his government respects the Canadian passport.

But, when the question of national security is involved, it reserves the right to act unilaterally.

Solicitor-General Wayne Easter told The Canadian Press the Arar case has been the subject of high-level negotiations between Ottawa and Washington.

"Friends can have differences and they've got to work to find ways of resolving those differences" Easter said, explaining the talks continue.

"We do have a major difference over this one particular instance, in terms of Arar. We do not want that to ever happen again."

Just a week ago, incoming prime minister Paul Martin spoke strongly of his plan to "get to the bottom" of the case of Arar, the Canadian man who claims he was tortured for close to a year in Syrian prison after being deported there by the United States.

Arar was released without charges and returned to Canada in October.

Martin told reporters last Tuesday, the need for cross-border information sharing had to be tempered by a respect for citizens' rights.

"If in fact we are going to have the kind of exchanges of information which are so important in terms of the security of North America, there is going to have to be an understanding that in fact the Canadian passport will be respected and that fundamental rights will be respected," Martin said.

But in response to Martin -- who will be sworn in as prime minister on Dec. 12 -- Cellucci said the fundamental U.S. priority will continue to be self-protection.

"We certainly respect the Canadian passport and we will continue to respect the Canadian passport, but we will do what we have to do to protect the security of the people of the United States," he said.

And that may not always sit easily with others.

"The president has no more solemn obligation than to protect the safety of the people of the United States. We will reserve the right to act unilaterally in very rare cases," Cellucci said.