At least 16 prisoners in a central Mexico jail were killed, and five more were injured in a riot that closed out a violent 2019 for the nation, officials said.

Zacatecas state security secretary Ismael Camberos Hernández informed the local press that officials confiscated four guns that they assume were introduced to the Cieneguillas state prison throughout prison visits Tuesday. He said the jail had been searched for weapons on Saturday and Sunday, and no guns were discovered.

The melee broke out nearby 2:30 p.m. Tuesday, and the jail was taken under control by 5 p.m., according to a comment from the state security agency.

Fifteen of the victims expired at the prison, and one died at a hospital.

One inmate was detained with a gun still in his possession, and the other three were found inside the prison, the comment said. Camberos said not all of the victims expired from gunshot injuries. Some were stabbed, and others hit with objects.

No guards or cops were injured, Camberos said. He did not give a possible motive, but such killings frequently involve score-settling between rival cartel members or conflict for control of the prison’s illicit business.

Mexico has a long history of deadly prison clashes. In October, six inmates were killed in prison in Morelos state.

In September, Nuevo Leon state closed the infamous Topo Chico prison, the site of many murders over the years. In February 2016, 49 prisoners died there during rioting when two factions of the Zetas cartel clashed.