MEXICO CITY (AP) — Authorities in northwest Mexico are searching for gunmen who ambushed a convoy carrying security forces, killing six police officers. At least two other people died.

José Rosas Aispuro, governor of Durango state, said Saturday that prosecutors are investigating the attack, which happened Thursday in the municipality of El Mezquital. Seven police officers were also injured.

Some vehicles abandoned by the attackers contained bloodstains, likely indicating casualties among the gunmen, said state prosecutor Ruth Medina.

The Sinaloa drug cartel is active in the area where the attack occurred.