By Felicia Schwartz and Robbie Whelan 

As U.S. Secretary of State Rex Tillerson and Homeland Security Secretary John Kelly arrived in Mexico on Wednesday, Mexico's foreign minister identified the Trump administration's new immigration guidelines as the main topic of high-level discussions set to begin this evening in Mexico City.

Foreign Minister Luis Videgaray said Mexico wouldn't accept any policy changes unilaterally imposed by the U.S., such as a new guideline ordering the deportation to Mexico of migrants from third countries.

"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," Mr. Videgaray said. "We won't accept it because we don't have to."

Messrs. Tillerson and Kelly were scheduled to meet Wednesday night and Thursday with Mexico's President Enrique Peña Nieto, Mr. Videgaray and the Mexican ministers of finance, interior, national defense and the navy. They were to discuss border security, law-enforcement cooperation, trade and other issues, the State Department said.

The trip follows the Trump administration's announcement Tuesday of major changes to the enforcement of immigration law at the border of Mexico and in the U.S. that make almost anybody in the U.S. illegally subject to deportation at any time. The directive also includes a review of all federal aid the U.S. provides to Mexico.

Mr. Videgaray said Mexico would use all legal means to protect the rights of Mexicans in the U.S., including calling on the United Nations and other international institutions.

News of the new deportation rules was posted quickly on Mexican media sites,l prompting an aggressive campaign by some Mexican officials, governors and public figures to fight the policy by jamming up U.S. immigration courts.

The timing of the latest immigration overhaul ratchets up tensions that the two allies have struggled to ease. Mr. Peña Nieto canceled a trip to the U.S. last month after Mr. Trump increased pressure on Mexico to pay for the wall Mr. Trump wants built along the southern U.S. border. The leaders also had a testy phone call last month, during which Mr. Trump reportedly told Mr. Peña Nieto that Mexico has "some pretty tough hombres" and that the country wasn't doing enough to fight cartels.

The two agreed in the call not to speak publicly about the border wall, according to Mexican officials familiar with the matter, but the issue is expected to come up in the discussions this week.

Adding to the strain, Mr. Trump is expected to demand a renegotiation of the North American Free Trade Agreement, which links the U.S., Mexican and Canadian economies.

Ahead of the visit, Mexican officials have suggested that if the U.S. pulls out of Nafta, it would affect all aspects of the U.S.-Mexico relationship.

"Logically, there wouldn't be incentives to continue collaborating on the issues most important to national security in North America, such as the issue of migration," Mexico's economy minister, Ildefonso Guajardo, told local newspaper Milenio in an interview published Tuesday.

Such remarks have surprised experts on the U.S.-Mexico relationship because they indicate the countries' longstanding friendship has deteriorated. In addition to having tariff-free cross-border trade, Mexico and the U.S. have collaborated for decades on efforts to fight drug cartels, police the border and prevent terror attacks.

Mr. Guajardo isn't scheduled to be in the meetings with Messrs. Tillerson and Kelly, a notable absence because his office is responsible for representing his country's trade interests and is expected to quarterback the renegotiation of Nafta for Mexico.

His U.S. counterpart, Mr. Trump's nominee for commerce secretary, Wilbur Ross, hasn't yet been confirmed by the U.S. Senate, nor has Robert Lighthizer, Mr. Trump's pick for U.S. trade representative, the official who would lead any Nafta renegotiation for the U.S.

Mexican officials want to have a comprehensive conversation about the two countries' relationship, in order to use issues including national security and migration as leverage for future conversations about Nafta, experts said. The U.S., in moving to examine aid to Mexico, also appears to be searching for leverage in future talks. The U.S. has pledged $135 million to Mexico this year.

"Mexico wants to link those issues in a way that has rarely been done before," said Duncan Wood, director of the Mexico Institute at the Wilson Center, a Washington think tank. "There's never been a need for that and Mexico has avoided it as much as possible, but now there is a need, so they're doing it."

Write to Felicia Schwartz at Felicia.Schwartz@wsj.com and Robbie Whelan at robbie.whelan@wsj.com

(END) Dow Jones Newswires

February 22, 2017 16:47 ET (21:47 GMT)

Copyright (c) 2017 Dow Jones & Company, Inc.