Mexican President Claudia Sheinbaum on Wednesday described the latest US tariff hikes on steel and aluminium imports, which doubled from 25 per cent to 50 per cent, as "unfair," "unsustainable," and lacking any "legal basis."

At her daily morning press conference, Sheinbaum said the measure, which applies to all countries except the United Kingdom, is unfair to Mexico because "Mexico imports more steel and aluminium than it exports."

Usually, "a tariff is imposed when there is a deficit," said Sheinbaum, but "we import more steel" so it is "unfair."

In addition, Mexico and the United States are partners in a free trade agreement, so from the Mexican government's perspective, the tariff "has no legal basis."

According to Washington, however, the tariff responds more to national security concerns than trade, noted the president, adding it is still unfair to apply it to Mexico, reports Xinhua news agency.

"It is being considered for reasons of US national security, and just yesterday, the White House spokesperson said there is very good collaboration on all fronts with Mexico, including the security issue. So, we don't believe it is justified," she said.

Finally, she added, the tariff will prove unsustainable "because just as ... there are many auto parts that cross from one side of the border to the other, the same occurs with steel."

Sheinbaum said she would meet with industry leaders during the day to present strategies, and her economy secretary, Marcelo Ebrard, was preparing negotiations with US authorities this week in anticipation of an agreement.

"Fifty per cent tariffs represent a significant impact on the steel and aluminium industry; 25 per cent already represented problems," she said.

With no agreement, her administration will announce what measures it will take next week, said Sheinbaum, adding it is not about "an eye for an eye," but about supporting the industry and the jobs it creates, which are "very important."

"We hope to reach an agreement. If we don't, then we will also announce some measures ... it's not a matter of revenge ... it's a matter of protection," the Mexican president said.