The bloodstained bodies of a man and a woman were found hanging from a bridge in northeast Mexico, along with threatening messages to people who report drug violence on social networks.

The messages lay near the two bodies, found half naked, alluding to websites set up for people to report drug violence in the area, police said yesterday.

"That will happen to all of them," read the text of one message signed with the letter 'Z' usually associated with the Zetas drug gang.

Nuevo Laredo lies in the northeastern state of Tamaulipas, on the US border, where the Zetas are blamed for many violent attacks.

The Zetas started as ex-elite army officers working as hitmen for the Gulf cartel in the 1990s. A split between the two is blamed for some of the country's most gruesome drug violence in recent years.

Mexico is one of the world's most dangerous countries for journalists and reporters have been silenced by threats or violence in some areas.

Citizens in those areas often rely on social networks for information about shootouts or other drug violence.