Hacker group says it will expose identity of Zetas gang and supporters in retaliation for the kidnapping of a group member

An internet video has threatened to expose allies of Mexico's Zetas drug cartel in the local police and news media unless the gang frees a kidnapped member of the international hacker movement known as Anonymous.

The YouTube message, which claims to be from Anonymous "Veracruz, Mexico, and the world", says it is "tired of the criminal group the Zetas, which is dedicated to kidnapping, stealing and extortion", and threatens to fight back with information instead of weapons. It said it knows of police officers, journalists, taxi drivers and others working with the Zetas.

The video refers to an unidentified person kidnapped in the coastal city of Veracruz, and says: "You have made a great mistake by taking one of us. Free him."

The hacker group, which has claimed responsibility for attacks on corporate and government websites worldwide, plans to act on Friday if the kidnapped activist is not freed or is harmed, according to the message.

"We cannot defend ourselves with weapons, but we can with their cars, houses, bars," the message adds, apparently alluding to properties owned by cartel supporters. "It's not difficult. We know who they are and where they are. Information is free," it says. "We do not forgive. We do not forget."

An official with the Veracruz state attorney general's office, who could not be named, said the office could not confirm the video's authenticity or the case of the kidnapping.

Veracruz, an oil state on the Gulf of Mexico with a major port of the same name, has seen a surge in drug violence in recent months in what authorities say is a battle between the Zetas drug cartel, which has controlled the territory for at least a year, and its rivals. Dozens of bodies have been discovered in recent weeks, including a 35-year-old dumped on a highway in rush-hour traffic in Boca del Rio city last month.

Two other internet postings since July have announced the arrival of the Mata Zetas group, or Zeta Killers, who authorities say are probably linked to the powerful Sinaloa cartel. Others have raised questions about whether the group's members are vigilantes or other rogue organisations taking justice into their own hands against the Zetas.

The message, presented by someone wearing a theatre mask that is a trademark of Anonymous, was reportedly uploaded to websites early this month, but was first reported on Friday on the website of the Stratfor global intelligence thinktank.

Stratfor, in its analysis of the video, said anyone exposed by Anonymous as a Zetas collaborator – accurately or not – would be targeted by rival gangs, and the Zetas could respond by attacking internet activists, even if they were not affiliated with Anonymous.

Three people have been killed recently in the northern states of Nuevo León and Tamaulipas by suspected Zetas who apparently believed the victims used the internet to spread information about the gang.