Washington - Republican presidential hopeful John McCain defended the "vital" partnership between the United States and Canada but warned that increased trade would come with increased security along the border, in a visit to US' northern neighbour on Friday.

McCain praised the North American Free Trade Agreement (NAFTA) for boosting trade and employment on all sides and - though never mentioning his Democratic rival Barack Obama by name - criticized protectionist elements back in his home country.

"We have to defend (NAFTA) without equivocation in political debate," McCain said at an economic club in the Canadian capital Ottawa. "Demanding unilateral changes and threatening to abrogate an agreement that has increased trade and prosperity is nothing more than retreating behind protectionist walls."

Obama has strongly criticized NAFTA for costing jobs in the United States and said he will seek to renegotiate the treaty to secure better labour and environmental protections. He has left open the option of pulling out if no deal with Canada and Mexico can be reached.

McCain by contrast is a staunch supporter of free trade and has warned that Obama's attempts to get a new deal would undermine confidence in the US trade position with other countries.

"If I am elected president, I have no doubt that America will honor its international commitments," he said.

But McCain also suggested more effort was needed in securing the two countries' borders, in light of the September 11, 2001, terrorist attacks.

"Our governments have made real progress in keeping our borders closed to terrorists and open to trade," he said. "We need to do an even better job managing the regular traffic across our border." (dpa)