Border Patrol Agents Accused of Abuses : Immigration: Mexican officials file complaints about three incidents since start of Operation Gatekeeper. U.S. disputes allegations.

In a sign that a federal border crackdown may be increasing tension at the U.S.-Mexico line, Mexican authorities alleged Tuesday that U.S. Border Patrol agents have physically and verbally abused illegal immigrants, one of whom remains hospitalized.

Grupo Beta, a plainclothes Mexican border police unit, has filed complaints through diplomatic channels about three incidents that allegedly occurred Sunday, the day after the Border Patrol launched a massive deployment titled Operation Gatekeeper.

In one case, six witnesses told Mexican police officers that U.S. agents on horseback told a handcuffed prisoner to run, then chased and knocked him down with one of their horses, according to Hugo Miguel Ayala, the Grupo Beta chief. The man, 21-year-old Antonio Gonzalez Ortiz of the state of Nayarit, was removed from the scene in an ambulance and was in fair condition Tuesday at San Diego’s Mercy Hospital.

“This is an abuse of authority,” Ayala said. “The cleanness of the operation is in danger of being dirtied. Our intention is not to harm relations, it is to correct the problems.”

However, Border Patrol officials gave a much different version. They said the handcuffed Gonzalez bolted on his own after being captured and fell into a ditch near the border fence, hitting his head. And Border Patrol authorities said they are concerned about the allegations, but have not been able to investigate because the Mexican Consulate has not filed formal complaints based on the Grupo Beta reports.

“If we receive a formal complaint, we will investigate,” said spokeswoman Ann Summers.

Summers said she did not know whether the pursuing horse came into contact with the fleeing suspect, but said of the allegation: “That does not sound like something (the agents) would do. The last thing you want is for them to run from you.”

U.S. officials anticipated that Operation Gatekeeper could produce conflicts, given resentment in Mexico about the Border Patrol’s crackdown and the inevitable potential for confrontation that comes with more arrests. Since the Border Patrol doubled the size of its deployment Saturday, the number of arrests in the Imperial Beach station area has also about doubled. Commanders have declared the buildup a success so far and emphasized the pains they have taken to avoid violence.

But the Grupo Beta allegations illustrate the risk for international tensions and the curiously ambivalent relationship between the Border Patrol and the Mexican unit.

The two forces cooperate effectively when it comes to fighting crime against migrants and quelling disturbances at the border. But Grupo Beta has consistently investigated and filed complaints about alleged abuses by U.S. agents during its four years of existence, angering Border Patrol commanders who say many allegations have not been substantiated.

A Mexican Consulate spokesman said Tuesday that a complaint had not yet been filed in the Gonzalez case because officials were waiting for the injured man to recover sufficiently to be interviewed. Gonzalez was injured after crossing into a canyon known as “the gravel pit” with a group including his wife, his brother and his sister-in-law, Ayala said.

In the other two cases, Grupo Beta officers allege that they saw a U.S. Border Patrol agent yell profanities Sunday evening over a vehicle loudspeaker at migrants near the Tijuana River levee, challenging them to cross.

And officers said they received a complaint from a migrant named Pedro Hernandez Lopez, 24, who showed up at the unit’s Tijuana headquarters with head injuries he claimed had been inflicted by a U.S. agent wielding a flashlight.