Police were searching for two prison guards and 41 inmates who disappeared after a pre-dawn jailbreak Thursday in the Mexican city of Matamoros across the border from Brownsville, Texas.
Prison director Orlando Saucedo Pinto has been put on temporary leave as investigators review how the prisoners broke out, Mexican prison officials told a news conference.
Prison staff are also being investigated, they said.
All but three of the prisoners who escaped had been charged under federal law but were being held at the state institution. State leaders in Mexico have complained in the past that they do not have facilities secure enough to accommodate more serious, federally charged prisoners.
Last year guards stood by as more than 50 prisoners walked out of another jail in northern Mexico.
U.S. Customs and Border Protection spokesman Eddie Perez in Brownsville said the agents at the border are on alert because the prisoners are at large.
"We do have a contingency plan in effect, and we will do anything that we can to ensure the safety of the traveling public and our officers," he said.
