Attack leaves police officer dead in northern Mexico
The officers were ambushed in the city of Vallecillo by gunmen riding in an SUV.
A third officer was reported missing following the attack, officials said.
Police in the city of Anahuac, meanwhile, found a clandestine grave containing four bodies at the Las Aves ranch.
The bodies were in an advanced state of decomposition and the victims have not been identified.
The coroner's office will perform autopsies on the bodies of the four men, officials said.