The US President, who has frequently criticised the existing deal, made the announcement on Monday.
Canada - the other member of Nafta - is yet to agree to the new terms and will hold more discussions on Tuesday.
Mr Trump had threatened to pull out of the deal, triggering a year of talks.
He demanded a renegotiation of the 1994 trade agreement, which he blames for a decline in US manufacturing jobs, especially in the car industry.
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