Assailants leave severed head outside Mexican news office Unidentified assailants have left a severed human head in a Styrofoam cooler outside the offices of a newspaper in Mexico's northern border state of Tamaulipas

MEXICO CITY -- Unidentified assailants have left a severed human head in a Styrofoam cooler outside the offices of a newspaper in Mexico's northern border state of Tamaulipas.

A hand-written sign left with the cooler threatened journalists.

The Expreso newspaper in the state capital of Ciudad Victoria reported Friday that the sign said: "For newspapers allied with million (dollar) agreements with (Gov. Francisco Garcia) Cabeza de Vaca, they are not going to save you and here is the proof."

The sign continued: "Keep staying quiet and you'll see."

In 2012, an explosive device aboard a car detonated outside the same Expreso office. No one was injured, but the blast broke windows and caused damage to the office and other buildings.

Tamaulipas has long been dominated by the Gulf drug cartel.