(Adds details of agenda, friction over aid, paragraphs 4, 14, 17-18, 20)
By Alexandra Alper and Anahi Rama
MEXICO CITY, Feb 22 (Reuters) - Mexico reacted with anger on Wednesday to what one official called "hostile" new U.S. immigration guidelines hours before senior Trump administration envoys began arriving in Mexico City for talks on the volatile issue.
The U.S. Department of Homeland Security unveiled plans on Tuesday 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, regardless of nationality.
The tension over the timing of the rules mirrors an outcry when President Donald Trump said on Twitter Mexico should pay for his planned border wall shortly before Mexican President Enrique Pena Nieto was due at a Washington summit in January.
However, White House spokesman Sean Spicer said in Washington U.S.-Mexico ties were "phenomenal right now" and that he expected a "great discussion." Other senior officials also put on a brave face, telling reporters the trip was aimed at building a close working relationship.
Trump, who took office last month, campaigned on a pledge to get tougher on the estimated 11 million illegal immigrants in the United States, playing on fears of violent crime while promising to build the wall and stop potential terrorists from entering the country.
U.S. Secretary of State Rex Tillerson landed in Mexico City on Wednesday afternoon. He was joined by Homeland Security Secretary John Kelly later for talks the White House said would "walk through" the implementation of Trump's immigration orders.
Kelly signed the guidelines issued by his department on Monday.
Mexico's lead negotiator with the Trump administration, Foreign Minister Luis Videgaray, said there was no way Mexico would accept the new rules, which among other things seek to deport non-Mexicans to Mexico.
"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," Videgaray told reporters at the Foreign Ministry.
He said the issue would dominate the talks on Wednesday and Thursday. Mexico will insist that the United States proves the nationality of any person it wants to deport to Mexico, he said.
"We also have control of our borders and we will exercise it fully," he said, adding that Mexico was prepared to go the United Nations to defend the freedoms and rights of Mexicans under international law.
"HOSTILE, UNACCEPTABLE"