Thirty Mexican marines have been arrested over the disappearance of an unspecified number of people in the north-eastern state of Tamaulipas in 2014, officials say.
Prosecutors say the victims went missing when the marines deployed in the border city of Nuevo Loredo.
About 85,000 people have disappeared in Mexico since 2006, when the government launched a war on drugs traffickers.
Criminal groups are behind most cases, but security forces are also blamed.
This is the largest detention of military personnel in relation to disappearances in recent years, and a blow to the Mexican Navy, considered the country’s most trusted security force.
The marines were handed over to the attorney general’s office last Friday “in compliance with arrest warrants… for the alleged crime of forced disappearance of persons”, the Navy said in a statement.
No details have been made public.
Tamaulipas, one of Mexico’s most violent states, has one of the highest rates of missing persons in the country. Many of the disappearances take place on roads leading to the US.
Enforced disappearances are rarely fully investigated in Mexico and almost all cases are left unsolved. Thousands of victims end up unidentified in morgues across the country or buried in clandestine graves.
Corrupt security forces are suspected of involvement in many of the disappearances, either to cover up wrongdoings that led to deaths or in collusion with criminal organisations who hold the victims for ransom, activists say.
In one of the most high-profile cases, 43 students disappeared in the southern state of Guerrero in 2014. The state prosecutor in the case said the students had been handed over by corrupt local police to a criminal gang, who killed them and burned their bodies.