Mexico has warned the US against imposing a unilateral tax on Mexican imports to finance a border wall, saying it could respond in kind.
Foreign Minister Luis Videgaray said the government could place tariffs on selected goods from US states reliant on exports to Mexico.
Earlier, US President Donald Trump vowed to start building the wall “soon, way ahead of schedule”.
The US government says it will start accepting design proposals next month.
The US Customs and Border Protection Agency says it will ask companies to submit proposals “for the design and build of several prototype wall structures” on or around 6 March.
A shortlist of the best designs will be drawn up by 20 March, after which bidders will be asked to cost their ideas.
Contracts are expected to be awarded by mid-April.
Addressing the Conservative Political Action Congress (CPAC) in Maryland on Friday, President Trump vowed to always put American citizens first and build a …
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