MEXICO CITY—Top U.S. officials arrived for talks here Wednesday to find a defiant Mexican government refusing to accept President Donald Trump’s tougher immigration and deportation policies.

“I want to make it emphatically clear that neither Mexico’s government or the Mexican people have any reason to accept provisions that have been unilaterally imposed by one government on the other,” Mexico’s Foreign Minister Luis Videgaray said at a ceremony on Wednesday.

“We won’t accept it because we don’t have to,” he added, in an apparent reference to U.S. plans to return illegal migrants to Mexico, regardless of their nationality.

Mr. Videgaray’s declaration spelled trouble for Secretary of State Rex Tillerson and Homeland Security Secretary John Kelly, who a White House official said were sent to “talk through the implementation” of Mr. Trump’s guidelines.

Mexico City’s objection was the latest blow to U.S.-Mexico relations, which have frayed amid Mr. Trump’s vow to build a border wall estimated to cost $21 billion at Mexico’s expense and his plan to renegotiate the North American Free Trade Agreement between the U.S., Canada and Mexico. The rupture resulted in the cancellation of a state visit last month by Mexican President Enrique Peña Nieto.