Republican front-runner John McCain warned on Friday that his Democratic rivals are jeopardizing Canada's military support for the U.S. by threatening to renegotiate the North American Free Trade Agreement.

McCain said national security and trade issues are "interconnected with each other."

"One of our greatest assets in Afghanistan are our Canadian friends. We need our Canadian friends, and we need their continued support in Afghanistan," McCain said.

"So what do we do? The two Democratic candidates for president say they're going to unilaterally abrogate NAFTA .... How do you think the Canadian people are going to react to that?''

During their Democratic debate in Ohio on Tuesday, both Barack Obama and Hillary Clinton suggested they would opt out of NAFTA unless there were renegotiations. At first, McCain characterized his rivals' positions as an abrogation of the trade deal, but later softened his language.

"Maybe they're not saying 'abrogate,'" he said, noting, "They're saying 'radically restructure.'"

"I think Canada would view that as a betrayal of the long years of negotiations that we agreed to."

NAFTA, which was implemented in 1994, replaced the Free Trade Agreement, which was signed by Canada and the U.S. in the 1980s. The new trade deal brought Mexico into the fold and has been blamed for job losses in states such as Ohio, a pivotal state in the Democratic primary race. Ohio has lost more than 200,000 jobs since 2001 and it's estimated as many as 900,000 manufacturing jobs were lost in the U.S. in NAFTA's first decade.

But Canadian officials say cross-border trade supports more than 275,000 jobs in Ohio alone. Economists also point out that NAFTA is not the sole factor when determining job losses. The effects of globalization and more efficient companies that do more with fewer workers have decreased the number of jobs.

McCain's attack on Clinton and Obama follows similar criticism he levelled earlier this week. Friday's remarks also came on the heels of a statement by U.S. President George Bush which rebuked the Democrats for criticizing NAFTA "to score political points."

The political rhetoric on all sides of the issue doesn't appear to be surprising some voters, though.

"These people only come here when they want a vote," said Youngstown, Ohio, resident Ken Croyle.

In Canada, the NDP has said that Ottawa should take advantage of any openings to renegotiate the deal. But Prime Minister Stephen Harper has said it would be unwise to reopen the deal which has benefited all three countries.

With files from The Associated Press