TORONTO (AP) _ Canada's refusal to join the coalition fighting in Iraq has upset and disappointed the United States and caused a ``bump in relations,'' U.S. Ambassador Paul Cellucci said Tuesday.

In a speech to a business breakfast and later comments to journalists, Cellucci said the Canadian position showed that Prime Minister Jean Chretien's government was less concerned about security threats than the United States.

``They support the global war on terror, but they're not supporting us fully,'' Cellucci said.

Raising his voice during his speech, he said the United States would respond immediately to any security threat in Canada.

``There would be no debate. There would be no hesitation. We would be there for Canada,'' Cellucci said. ``That is why so many in the United States are disappointed and upset that Canada is not there for us now.''

Canada cited the lack of U.N. backing for war in Iraq in declining to join the Iraq coalition, but Chretien's government has been a major participant in the U.S.-led war on terrorism. It will send more than 1,000 troops to Afghanistan this year.

Jim Munson, Chretien's director of communications, characterized the Canadian stance on the Iraq war as a difference of opinion between ``best friends.''

``We feel we are playing a significant role in the war against terror,'' Munson said.

Cellucci called it ``helpful'' that Canadian Foreign Affairs Minister Bill Graham said Canada could eventually join the war in Iraq.

He also noted that Canada's role in the fight against terrorism includes Canadian warships in the Persian Gulf and some Canadian military planners working with U.S. and British forces in the Gulf region.

``Ironically, the Canadians indirectly provide more support for us in Iraq than most of those'' 46 countries in the coalition fighting against Saddam Hussein's regime, he said.

The ambassador called the issue a ``bump in relations'' between the North American neighbors and strategic allies that share the world's largest trade partnership, worth more than $1 billion a day.

He said there could be some repercussions against Canada in U.S. policy, but he refused to elaborate.

Cellucci stressed Canada's importance to the United States and said the two nations continue to work together. He noted that the two nations have always had differences, such as the United States' current punitive duties on Canada's softwood lumber exports.

``Our ties are deep and long-standing,'' Cellucci said. ``We are dependent on each other.''