Six Mexican prison guards have been found shot dead outside one of the country's maximum security prisons.
Their bodies were discovered outside the Matamoros Penitentiary, on Mexico's northern border with Texas.
This comes after a government crackdown on prisons over fears that drug gangs wield too much power inside jails.
The corpses of the six prison guards were found inside a vehicle riddled with bullet holes just 1km from the prison watchtower.
Some of the officers had been blindfolded before they were murdered.
Using helicopters, dozens of troops arrived to seal of the penitentiary, which is just across the border from Brownsville, Texas.
It is only a week since more than 750 federal soldiers and police were called into take control of another high security prison, at La Palma near Mexico City.
This came after a spate of murders and rumours that two powerful drugs lords, Osiel Cardenas and Benjamin Arellano Felix, were joining forces inside the prison.
Some inmates had been transferred from La Palma north to Matamoros to try to break up the group.
Interior Secretary Santiago Creel directly linked the events, saying: "These reactions we are seeing are precisely because we are cleaning up the prisons."
President Vicente Fox has vowed not to be intimidated by this latest challenge to the state's authority.
He has pledged to wage "the mother of all battles" against organised crime and drug trafficking now present within federal prisons.
Posted By: Redneck Texan