The US government has pledged to commence the formal process of renegotiating the North American Free Trade Agreement (NAFTA) in the next few weeks.

US commerce secretary Wilbur Ross has stated that within a "couple of weeks", he will send a letter notifying Congress that president Donald Trump's administration will launch NAFTA negotiations in 90 days.

This is part of the process that gives the US president fast-track authority on trade pacts, with the head of state being required to outline the administration's goals and consult with key committees in the House and Senate before talks can commence.

Full-scale negotiations between the US and its NAFTA partners Canada and Mexico are unlikely to commence until later this year, with President Trump expressing a willingness to pull out of the pact completely if new terms that are more favorable to the US cannot be reached.

Describing NAFTA as a "very old agreement", Mr Ross said: "As a minimum it needs an update, and also there arguably were some sections of it that didn't work out quite the way they had been expected to."