DONALD Trump has said the trade tariff he has slapped on Mexican imports to the United States will gradually increase to 25% “until the illegal immigration problem is remedied”.

The US president announced a 5% tariff on Thursday as his administration looks for new levers to pressure Mexico to crack down on central American migrants trying to cross the US border.

It appears Trump is determined to keep the issue at the top of his agenda, even if it risks upending other policy priorities, such as the United States-Mexico-Canada Agreement (USMCA), a trade deal that is the cornerstone of his legislative agenda and beneficial to his re-election effort.

Mexican president Andres Manuel Lopez Obrador said his foreign relations secretary will lead a delegation to seek a peaceful and negotiated solution to the border issue.

Lopez Obrador said in a public letter addressed to Trump that “social problems are not solved with duties or coercive measures,” and alluded to the US’ history as a nation of immigrants, saying: “The Statue of Liberty is not an empty symbol.”

Lopez Obrador wrote that Mexico is doing its part to avoid migration through its territory as much as possible, without violating human rights. The Mexican leader also urged Trump to “please, remember that I do not lack valour, that I am not a coward nor timorous but rather act according to principles”.

Trump made the tariff announcement on Twitter after telling reporters earlier that he was planning “a major statement” that would be his “biggest” so far on the border. He tweeted: “On June 10, the United States will impose a 5% Tariff on all goods coming into our Country from Mexico, until such time as illegal migrants coming through Mexico, and into our Country, STOP. The Tariff will gradually increase until the Illegal Immigration problem is remedied.”

Trump has accused the Mexican government of not doing enough to halt the flow of asylum-seekers from countries including El Salvador, Honduras and Guatemala. But the sudden tariff threat comes at a peculiar time, given how hard the administration has been pushing for passage of the USMCA, which would update the North American Free Trade Agreement.

It is only two weeks since Trump lifted import taxes on Mexican and Canadian steel and aluminium, a move that seemed to clear an obstacle to passage of his North American trade deal, and the same day that both the Mexican government and the Trump administration began the process of seeking ratification. The deal needs approval from politicians in all three countries for it to be ratified. In late March, Trump threatened to shut the entire US-Mexico border if Mexico did not immediately halt illegal immigration. Just a few days later, however, he backed off , saying he was pleased with steps Mexico had taken in recent days. It was unclear what Mexico had changed.

During a briefing call with reporters on Thursday, administration officials said there were several things Mexico could do immediately to prevent the tariffs from kicking in, including securing their southern border with Guatemala and entering into a “safe third country agreement” that would make it difficult for those who enter Mexico from other countries to claim asylum in the US.

Acting White House chief of staff Mick Mulvaney said: “We’re going to judge success here by the number of people crossing the border and that number needs to start coming down immediately.”

He insisted tariffs were completely separate from the USMCA because one related to trade and the other immigration. The White House said the tariff will increase to 10% on July 1, to 15% on August 1, to 20% on September 1 and to 25% on October 1.