VOA News Center Associate Producer Jesusemen Oni contributed reporting from Washington. Mexico's president responded to U.S. tariff threats with caution again Friday, urging "dialogue" over "coercive measures" in the latest conflict over the two countries' migration policies."I want to reiterate that we are not going to fall into any provocation; but we are going to be prudent, and we are going to respect the authorities of the United States and President Donald Trump," said Mexican President Andres Manuel Lopez Obrador. "We think that any conflict and bilateral relations should be solved with dialogue, with communication. The use of coercive measures does not lead to anything good," he added. His statement Friday morning followed a two-page letter to Trump made public late Thursday, similar in tone, responding to Trump's announcement on Twitter earlier in the day that the U.S. would begin imposing an escalating tax on imports from Mexico."On June 10th, 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," Trump tweeted. Until "the illegal immigration problem is remedied" tariffs will continue to rise monthly, going as high as 25% by October 1. U.S. border agents have apprehended an increasing number of people, largely from Central America, who crossed the southern U.S. border without authorization in recent months. In contrast to previous spikes in arrivals, recent groups have included a large number of children, prompting U.S. officials to scramble to support families and children traveling without parents — some of whom are seeking asylum.In an indication of the pressing demands at the border, U.S. Customs and Border Protection solicited bids for the purchase of tens of thousands of baby diapers, wipes and bottles this past week, according to documents reviewed by VOA on a government contracting website.Mexico has the "absolute ability and authority to do a lot more than they're doing," White House press secretary Sarah Sanders told reporters Friday.Reaction from MexicoLopez Obrador posted a letter to Twitter after Trump's announcement that said, "Social problems are not resolved with taxes or coercive measures."Trump's announcement of the new tariffs came on the same day Mexico began the formal process of ratifying the United States-Mexico-Canada Agreement on trade.Lopez Obrador said he was sending his foreign minister, Marcelo Ebrard, to Washington to try to negotiate a solution. Mexico's deputy foreign minister for North America, Jesus Seade, says such tariffs would be disastrous, expressing more alarm than the Mexican president."If this threat is carried out, it would be extremely serious," he told reporters. "If this is put in place, we must respond vigorously."For one trade expert, who previously served as Mexico's ambassador to China — a top trading partner for that country and the U.S. — the timing of Trump's tariff statement raises questions about the future of the USMCA."By mixing two things — immigration and now, just lately, drug flow — with trade, I think it confuses the issue," said Jorge Guajardo, a senior director at the Washington-based international trade consulting firm McLarty Associates.The trade deal "was a triumph for all three countries, and now, of course, that all comes into doubt," Guajardo added.Marking progressSome Republican members of Congress but no Democrats were consulted about the plan, according to acting White House Chief of Staff Mick Mulvaney.Asked in a hastily arranged conference call with reporters about benchmarks Mexico would need to achieve to have the tariffs lifted, Mulvaney said there needs to be significant and substantial reductions in arrivals from Central America crossing into the United States."We're going to take this and look at it on a day-to-day and week-to-week basis," said Mulvaney. "We are interested in seeing the Mexican government act tonight, tomorrow."Trump has repeatedly accused Mexico of not doing enough to stop Central American migrants from traveling through the country on their way to the United States.The U.S. system, however, is not infallible. While the country has increased its apprehension rate at the border in recent years, U.S. border agents stop an estimated 65% to 80% of people crossing into the country without authorization, according to a 2018 DHS report.