Mexican federal police on Thursday rescued 79 Central Americans in the violent border city of Reynosa in the northeastern state of Tamaulipas, a day after authorities freed another 34 people in the same state, the Security Ministry said in a statement.

The federal police exchanged fire with an armed group who managed to flee the scene in a van, after which the police rescued 35 Guatemalans, 27 Salvadorans and 17 Hondurans, the ministry said. Four Mexicans were also rescued with the group of Central American migrants.

"Personnel from the National Immigration Institute were called in and they verified that the persons did not have legal permission to be in the country," the statement added.

Officials are separately investigating the disappearance of 22 passengers, thought to be migrants, who were kidnapped by armed men from a bus in Tamaulipas last week.

For years, Tamaulipas has suffered high levels of murders and disappearances amid clashes between violent criminal gangs.

In August 2010, 72 undocumented migrants from Central and South America were murdered by the Zetas gang at a ranch in Tamaulipas. A year later, nearly 200 corpses, many of them Mexicans, were found in mass graves in the area.

Mexico is also grappling with corruption within its migration authorities and is investigating reports that border agents are extorting migrants, according to Interior Minister Olga Sanchez Cordero.