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(Image: Twitter/@Miut3)

A Mexican drug cartel has tracked down and murdered a social media journalist who campaigned to expose local gang violence - then used her Twitter account to post photos of her dead body to her followers.

María del Rosario Fuentes Rubio used a pseudonym to report on organised crime in the Mexican state of Tamaulipas - where extortion, shootouts, kidnappings and executions are rife.

Very few of these crimes get reported in the mainstream media because the cartels - the Zetas and Gulf Cartel - use fear and intimidation to order a media blackout.

This means that local citizens turn to Facebook and Twitter to share reports of crime and corruption.

María helped run an influential citizen news site called Valor por Tamaulipas (Bravery for Tamaulipas), which had a huge social media following, with more than 510,000 Facebook fans and 100,000 Twitter followers.

(Image: Getty Images)

The site would post photos identifying cartel members, missing persons messages and notifications of crimes carried out by the cartels.

In an attempt to stay safe, she used the pseudonym of Felina (Catwoman). When on Twitter, she used the handle @Miut3. Her posts would urge people to be brave and speak up about gang crime.

In early October, María started receiving threats on Twitter, but she remained defiant.

However, on 16th October the tone of her account completely changed; the cartel had identified her, tracked her down and were using her account to warn others not to speak out.

(Image: Valor por Tamaulipas)

The first tweet outed her: "Friends and family, my real name is Maria Del Rosario Fuentes Rubio, I’m a doctor and today my life has come to an end.”

They then posted two photos: the first of a woman looking in the camera. The second, that same woman dead on the floor with a bullet wound to the head.

Another tweet warned others not to make the same 'mistakes':

"Shut down your accounts, do not risk your families’ lives as I have done. I ask your forgiveness.”

Mexico is an extremely dangerous place for journalists and anti-cartel campaigners to operate.

Seven journalists have now been murdered in the last two years, according to Reporters without Borders.

"Reporters Without Borders is shocked by the murder of María del Rosario Fuentes Rubio and urges the government to investigate thoroughly to identify those responsible as quickly as possible," said Virginie Dangles, the organisation's deputy programme director.