A violent clash at a prison in Mexico's northwestern state of Sinaloa killed 10 people and injured 16 others on Thursday, prompting a security operation involving federal and state forces.
The confrontation erupted during morning family visiting hours at the El Castillo Penitentiary Centre in the port city of Mazatlan, according to state authorities.
Nine inmates and one family visitor were killed, while 16 prisoners were transferred for medical treatment.
Sinaloa's Secretary of Public Security, Sinuhe Tellez, confirmed in a video posted on social media that the visitor killed during the violence was a minor.
Authorities have not disclosed how the victims died, although local media reported that inmates used firearms during the confrontation.
Personnel from Mexico's army, National Guard, navy and state security forces entered the penitentiary following the violence.
The federal security cabinet subsequently confirmed that the facility, which houses approximately 1,800 inmates, was under control.
Security personnel remained stationed at the prison as a precaution.
Officials suspended family visits, while social workers began contacting relatives of those killed.
Tellez said the remaining prison population was safe.
The deadly confrontation occurred against a backdrop of persistent violence in Sinaloa, where rival factions of the Sinaloa Cartel have been fighting since September 2024.
The conflict pits the sons of convicted former cartel leader Joaquín Guzmán, known as Los Chapitos, against followers of detained cartel figure Ismael Zambada.
Authorities have not established whether Thursday's prison violence was connected to the cartel conflict.
The incident follows another deadly prison riot in May in Culiacan, Sinaloa's capital, which killed seven inmates and injured another.
Analysts have identified overcrowding, insufficient staffing and extensive pretrial detention as factors contributing to corruption and violence within Mexico's penitentiary system.
Official figures show the country's prison population reached 261,388 in February.
The latest deaths also come as Mexico faces pressure from the Trump administration to intensify operations against drug cartels.
The US State Department lists Sinaloa among six Mexican states Americans are advised not to visit because of security concerns.