People detained at an overcrowded federal immigration camp in Mississippi were sickened by a mystery gas leak, then denied medical care when they complained of headaches and other symptoms, it has been alleged.

A lengthy power outage at Adams county detention center, an Immigration and Customs Enforcement (ICE) facility run by the private operator CoreCivic, also left it without air conditioning for two days this week, according to one detainee who contacted the Guardian through his family.

As a result, he said, people detained there were forced to spend hours outside in near 100F heat in blazing sunshine and with no shade, or left to swelter inside in cramped cells.

Tensions at the center, he said, were rising, and more arguments and physical altercations were taking place between people there, leaving him and others fearful of violence that he said inadequate staffing levels would not be able to handle.