Mexico ? A shark injured a 49-year-old American surfer Saturday off the Pacific coast of Mexico, in the third attack in a month.

The Mexican Navy deployed personnel to warn people about sharks at beaches in Zihuatanejo, a resort northwest of Acapulco, according to a Navy official who spoke on condition of anonymity because he was not authorized to release the information.

He said authorities have not closed beaches in Zihuatanejo, but people were being advised against swimming.

A day earlier, a 21-year-old Mexican surfer was killed by a shark off a nearby beach. The two attacks came a month after a shark killed a San Francisco man surfing in the same area.