At least four inmates used a rope to escape from the prison in Culiacan, the capital of the northwestern Mexican state of Sinaloa, while guards slept, the Public Safety Secretariat said.

The escape occurred early Monday, the secretariat said.

Initial estimates put the number of escapees at 12, but officials later revised the number downward to four.

The inmates used a rope to lower themselves out of the prison and then cut through the fence using shears, the secretariat said.

The guards assigned to the cell block are being investigated to determine whether they aided the escape, prison officials said.

One of the escapees had tried to break out of the prison on May 18, the secretariat said.