Senior envoys of President Donald Trump are likely to receive a chilly reception in Mexico on Wednesday, after the United States issued new immigration guidelines that deeply angered its southern neighbor the day before bilateral talks.

Trump's administration on Tuesday unveiled plans to consider almost all illegal immigrants subject to deportation, and will seek to send many of them to Mexico if they entered the United States from there – even if they're not Mexicans.

Many illegal border-crossers begin their journeys in Guatemala or other Central American countries, first sneaking into Mexico and then traveling the length of that country on their way to the U.S.

U.S. Secretary of State Rex Tillerson and Department of Homeland Security Secretary John Kelly are due to arrive in Mexico on Wednesday afternoon for talks on security and immigration.

Luis Videgaray, Mexico's minister of foreign affairs (left) said Wednesday that U.S. President Donald Trump (right) can't deport illegal border-crossers to Mexico if they aren't Mexican citizens

White House Press Secretary Sean Spicer insisted that the U.S. can force countries to take their people back, but didn't mention cases where non-Mexicans enter the U.S. from Mexico

Mexico's lead negotiator with the Trump administration, Foreign Minister Luis Videgaray, said there was no way Mexico would accept the new 'unilateral' rules, which among other things seek to deport non-Mexicans to Mexico.

He said the issue would dominate the talks, taking place on Wednesday and Thursday.

'I want to say clearly and emphatically that the government of Mexico and the Mexican people do not have to accept provisions that one government unilaterally wants to impose on the other,' he told reporters at the foreign ministry.

'We will not accept it, because there's no reason why we should, and because it is not in the interests of Mexico.'

Another senior Mexican official, Roberto Campa, who heads the human rights department of the interior ministry, said Videgaray was referring to the plan to deport non-Mexicans to Mexico, calling it 'hostile' and 'unacceptable.'

White House press secretary Sean Spicer insisted Wednesday that 'any country who has a citizen that comes to the country and that we sent back, we'll make sure that they comply with this.'

He didn't mention, however, cases where the U.S. deports illegal immigrants to nations other than their countries of origin.

The Department of Homeland Security guidance to immigration agents is part of a broader border security and immigration enforcement plan in executive orders that Republican Trump signed on Jan. 25.

Trump has vowed to build a wall on the U.S. southern border, slap a hefty tax on Mexican-made goods entering the country and pull out of a trade deal with Mexico if he cannot renegotiate it to benefit the United States.

Secretary of State Rex Tillerson has gone to great lengths to avoid attracting attention, but that will end with his visit to Mexico

Secretary of Homeland Security John Kelly will begin his visit in Guatemala, which serves as a conduit for northbound illegal immigrants and narcotics

Mexican President Enrique Peña Nieto canceled a planned January meeting of the two leaders in Washington after Trump said his counterpart should not attend if he was unwilling to pay for the wall.

Despite the tensions, senior Mexican and American military and interior officials spoke this month in a sign that communication remained open between the two countries.

The Mexicans were hoping for a bit more calm, less vitriol and more constructive talk this week after months in which U.S. President Donald Trump has hammered Mexico.

Tillerson and Kelly are widely seen as less combative than their boss. But many Mexicans are starting to question the point of even talking to a suddenly confrontational U.S. government.

Kelly is starting his visit Tuesday in neighboring Guatemala, which also has a large immigrant population in the United Sates, also serves as a conduit for northbound drugs and also depends on the U.S. for anti-crime assistance.

A woman holds up a banner that reads in Spanish: 'Against Trump', during a march demanding respect for Mexico and its migrants in Mexico City on Sunday

Kelly will offer Guatemala little reassurance on deportations: He will visit a repatriation center where deported migrants are currently processed when they return on flights from the United States.

But it is Mexico that has to most to hope for – or lose – from the talks.

Mexico is entering a phase in which, at Trump's insistence, it will have to re-negotiate the North American Free Trade Agreement. That could imperil the export manufacturing sector that has become crucial to Mexico's economy since NAFTA took effect in 1994.

But it also could let Mexicans discuss restrictions on billions of dollars in American farm exports, as well as measures to ensure to U.S. oil and gas, a topic that was kept out of the original trade pact when Mexico jealously guarded its oil.

Mexico now imports huge amounts of gas and gasoline and officials now hope they can get the energy sector written into NAFTA. Tillerson, as the former head of ExxonMobil, may be just the person to do it.

'Tillerson, in his favor, would welcome what the Mexicans have been arguing have been arguing for, which is modernization or updating of the treaty including the energy sector,' Federico Estevez, a political science professor at the Autonomous Technological Institute of Mexico, told the Associated Press.

'Given his Exxon past, that would make sense that he would see the virtue in that.'

Tillerson and Kelly will meet with Mexican President Enrique Peña Nieto, who canceled a planned January meeting with President Donald Trump

Tillerson, who arrives Thursday, made friendly noises during his confirmation hearings, saying 'Mexico is a longstanding neighbor and friend of this country.'

Kelly, too, has sounded cooperative. After meeting with Mexican officials recently, Kelly he said his department is committed to work with Mexico on 'common economic and security opportunities and challenges, such as border security, migration management, repatriation and cross-border trade.'

Still, there are reports that the Trump administration might help finance a border wall by stripping away funds it gives Mexico under the Merida Initiative, a pact signed with then-President George W. Bush aimed at attacking drug trafficking and other security threats within Mexico.

Since 2014, Mexico has stepped up enforcement on its southern border to stem the flood of Central American migrants who have streamed through Mexico to get to the United States even as Mexican migration northward has stalled.

A policy memo published Tuesday by the Department of Homeland Security indicated U.S. authorities now want to send some of those Central Americans back to Mexico instead of their home countries even while they wait for their asylum or deportation proceedings to finish in the U.S.