MEXICO CITY (Reuters) - Twenty-two passengers kidnapped by armed men from a bus in northern Mexico last week may be migrants, a state government official said on Monday.

The gunmen had let the rest of the passengers go unharmed after intercepting the bus in the northeastern state of Tamaulipas last Thursday.

Mexican authorities have not been contacted by any family members of the missing, suggesting they may be migrants, state security spokesman Luis Alberto Rodriguez said in an interview.

“There are no complaints, there are no relatives who are filing claims for the people who are missing,” he said.

Rodriguez said later that following investigations, authorities had registered 22 people missing, three more than previously reported.

Tamaulipas has for years 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 Mexican, were found in mass graves in the area.