Stephen Harper addressed the revived debate about whether Canada should join the U.S. ballistic missile defence system, declining to rule out this country's participation in light of shifting global events.

Speaking after a Group of Seven meeting in Brussels, the prime minister said Canada has not changed its position.

But, he added, Canada is taking note of "changes occurring in the world."

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"Policies like this are examined on an ongoing basis to see whether they serve the security interests of Canadians," Mr. Harper told reporters in Brussels.

"It was our judgment in the past that Canadians did not need the security of participation in the anti-ballistic missile defence system. Obviously there are changes occurring in the world and we will continue to examine whether that does or does not serve Canadian interests and we will make whatever decision is in the best security and safety interest of Canadians."

The governing federal Conservatives appear to be trying to gauge the Canadian public's appetite for joining the U.S. missile defence program.

Speaking publicly last month, James Bezan, the Conservative parliamentary secretary to the Minister of Defence, said there is concern about the accuracy of missiles being developed by rogue states that might target the United States but end up striking Canada.

Tory-dominated committees in both the Senate and House have been examining the merits of the U.S. program, which former Liberal Prime Minister Paul Martin opted against joining in 2005.

Last month, two former Liberal defence ministers appeared before a Senate committee to say they feel the time is right for Canada to join the U.S. missile shield program.

Bill Graham and David Pratt said the time is right to revisit the matter.

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In late May this year, it was Mr. Martin's defence minister who urged Canada to change course.

"The ultimately security of Canada within the North American context is better off when we're participating with the Americans in the development of these systems that are designed to protect North America as a whole," Mr. Graham told reporters in May after his appearance at the Senate committee.

Both Mr. Graham and Mr. Pratt, who held the post during Jean Chrétien's administration, say they were hamstrung in their day by antipathy among Canadians toward then-U.S. president George W. Bush.

Mr. Bush, a right-wing Republican, lost ground in popularity after leading a coalition of countries into a war in Iraq.

"It was very much in the context of the Bush years and the Bush administration, and we kind of forget that. Just to put it bluntly, if it had been President [Barack] Obama asking for it with this approach, you never know – we might have said yes," Mr. Graham said in May.