Plans to modernise the North American Free Trade Agreement (Nafta) will take centre stage when the leaders of the US, Canada and Mexico meet on Monday.

The 14-year old agreement, which has generated $700 billion in cross-border trade, has come under increasing fire in the US where it is seen to have cost jobs.

The trade deal is a cornerstone of a broad-ranging Security and Prosperity Partnership agreed by the trio in 2005.

Thousands of protesters are gathering in Quebec ahead of the two-day summit.

Police have established a 25km security cordon around the resort complex, a 90-minute drive from Ottawa, where President George W Bush, Mexico's President Felipe Calderon and Canada's Prime Minister Stephen Harper are to meet.

Critics of Nafta and other free trade deals argue that they have destroyed jobs in poorer countries and damaged the environment.