(CNN) -- The 129 inmates who escaped from a northern Mexico prison did not flee through a tunnel, as authorities first reported. They walked out the front door.
Federal and local authorities launched a manhunt after the inmates escaped Monday in Piedras Negras, across the border from Eagle Pass, Texas.
Authorities arrested 16 employees, including the prison director, after the escape.
Politician Manlio Fabio Beltrones said the prison break highlights a larger issue in Mexico.
"The crisis in the Mexican prison system is serious and must be addressed urgently," Beltrones said.
Mexican President Felipe Calderon condemned the escape, calling it "deplorable" in a series of Twitter posts Tuesday.
"In the past six years, more than 1,000 inmates have escaped from state prisons. From the federal prisons, not one," he wrote.
The largest escape during Calderon's six-year term occurred in December 2010, when 151 inmates escaped from a local prison in the Mexican border city of Nuevo Laredo.
Authorities originally said the inmates in the latest escape slipped through a 23-foot tunnel, sliced through a chain-link fence and ran through an empty lot.
But they released new information saying the inmates went through the front door.
"It is hard to believe that they went through that tunnel," said Jose Luis Moran, the public safety secretary for the Mexican state of Coahuila.
Officials originally said that 132 inmates had escaped but adjusted the figure to 129 after finding three inmates hiding in another part of the prison.
Police set up blockades on roads leading to the Mexico-U.S. border. U.S. Customs and Border Protection placed its officers and agents in the area on alert, a homeland security official said.
"At this point, CBP has no reports of escapees attempting to cross the border. We will continue coordinating with our Mexican counterparts as we monitor this situation," the source said.
CNN en Español's Mario Gonzalez and Rey Rodriguez and CNNMexico.com contributed to this report.