Mexico has warned US President Donald Trump that tariffs on Mexican goods could worsen illegal immigration to the US and end up hurting both countries.
The warning came as Mr Trump tweeted that Mexico could "stop the flow of people and drugs" across the border "if they want".
Mexican and US officials are in talks while Mr Trump is in the UK.
The president has said he plans to impose a 5% duty on all Mexican goods from next week.
The tariff would then rise by 5% every month until it reached 25% in October if Mexico did not act to halt migrants coming across the southern border.
It comes as the US fights a trade war on several fronts, including with China. Mr Trump has unusually used tariffs in diplomatic disputes since taking office.
What is Mexico's position on this?
Speaking in Washington DC on Monday, Mexican officials insisted they were acting to stem the flow of people, many of whom are trying to reach the US so they can claim asylum.
Mexico's Foreign Minister Marcelo Ebrard told reporters they remained committed to tackling the issue, and warned that if they did "nothing", a quarter of a million migrants would reach the US this year, according to Reuters news agency.
He also rejected a suggestion Mexico could become a "safe third country" as "unacceptable". Some US officials want Central American migrants seeking asylum in the US to apply for it in Mexico instead, according to Reuters.
Meanwhile, the country's agriculture minister said they estimated the cost of the tariffs on the agricultural sector alone to be some $117m (£92m) a month in both countries, Reuters said.
Why is the US doing this?
US Commerce Secretary Wilbur Ross, who met with Mexico's Economy Secretary Graciela Marquez, said he had told her that Mexico needed to step up its efforts to address illegal immigration.
Mexico was the second largest supplier of goods to the US last year, with imports totalling $352bn (£275bn), according to Goldman Sachs.
However, relations have been strained, with President Trump saying Mexico is not doing enough to stop people reaching the southern border.
As a result, Mr Trump declared a national emergency at the US-Mexico border in February.
He said it was necessary in order to tackle what he claimed was a crisis with thousands of undocumented migrants crossing the US southern frontier.
Mr Trump's tariff threat came as US officials have also been pushing for passage of the United States-Mexico-Canada Agreement, an update to the North American Free Trade Agreement - and US lawmakers have warned the latest moves could hinder its progress.