CBP has long been aware of the encampment. But during the Obama administration former Tucson Sector Chief Manuel Padilla and the group had come to an informal agreement that CBP would not raid the camp, which provides water and medical treatment to anyone who crosses the desert. On Thursday, temperatures in the area soared above 105 degrees.

The Customs and Border Protection Agency’s Arizona office also tweeted about the incident, releasing photos of migrants being arrested and announcing that the arrests were of Mexican nationals for immigration violations.

The arrests came during a heat wave and after several days of heightened surveillance of the camp, which is run by No More Deaths. In a tweet Thursday evening, the organization said “30 armed agents entered camp w at least 15 trucks, 2 quads and helicopter to apprehend four patients receiving care.” Tucson.com first reported on the arrests Thursday evening.

TUCSON — Border Patrol agents on Thursday arrested four undocumented immigrants receiving medical care at an encampment run by humanitarian activists a few miles north of the Mexican border near Arivaca, Arizona.

The agreement between CBP and the aid organization dates to 2013 when, according to No More Deaths, border patrol agreed to treat the group as a medical facility under international Red Cross standards, which would bar them from arresting immigrants seeking medical attention.



The agreement allowed the organization to continue providing medical assistance to immigrants — and meant that those crossing the border wouldn’t be too afraid of arrest to seek out help from the activists. That deal, which No More Deaths described as a “good faith agreement,” no longer appears to be operative, and could be bad news for immigrants crossing the border.

According to an unsigned copy of the agreement provided to BuzzFeed News by No More Deaths, the deal provided the group with the ability to conduct medical care for immigrants without fear that they would be interfered with. It also required Border Patrol officers to be trained on "the Red Cross Code of Conduct, the principles of our relationship, and respect for the independent mission of the humanitarian organizations."



Maryada Vallet, a spokesperson for No More Deaths, said the raid "feels like a direct and targeted attack on the humanitarian assistance we are providing during these hot and deadly days."

According to the group, CBP officials informed them that agents had been tracking the immigrants crossing the border for 18 miles and only arrested them after they were in the camp receiving treatment.

In a statement CBP said Border Patrol said they wanted to question the four migrants because they were detected entering the US wearing camouflage and walking north on a known smuggling route. The agents tracked them to the No More Deaths camp and reached out to representatives from the group to help them question the four migrants after noticing they didn't leave the area.

No More Deaths refused, prompting Border Patrol agents to serve the camp with a search warrant before arresting four Mexican nationals for immigration violations.

The agency pointed to a similar incident a month ago in which eight people turned themselves over to agents. Two of them had unspecified criminal records in the US and another two required medical care at a hospital.

Eva Lewis, a volunteer with No More Deaths, said they never turn anyone over to Border Patrol. In the incident that occurred a few weeks ago the eight migrants decided to turn themselves into agents.

“They made the decision to turn themselves into custody, that is not the same as anyone turning anyone else into law enforcement,” Lewis said. “Sometimes people decide to go into custody for a variety of reasons. When they make that decision we talk with them about the possibilities of applying for asylum and the risks of going through operation streamline.”

The desert region surrounding Arivaca is one of the more dangerous sections of the border, with temperatures well above 100 degrees during the summer months and extremely rugged terrain. Immigrants crossing through the desert routinely go missing, and aid workers discover hundreds of bodies every year along the trails used by immigrants.

If the camp is shut down, or if immigrants avoid it out of fear of being arrested, it could mean more people in need of urgent care will go without and ultimately die.