The two embassy employees were hospitalized, one with a leg wound and the other hit in the stomach and hand, according to a government official who spoke on condition of anonymity. Another official said they were in stable condition. The U.S. Embassy had not released details of the shooting or the names of the victims nearly 12 hours later.
The Navy said in a written statement that federal police shot the U.S. vehicle, but its description of the incident left out key details of how the shooting occurred. It said at least four vehicles opened fire on the Americans' sport utility vehicle on a road south of Mexico City, but did not make clear if any of the four carried federal police officers.
A U.S. official who was briefed on the shooting said, however, that all the shots were fired by federal police, of which at least 12 officers were being held for questioning by Mexican authorities. The U.S. Embassy employees were on their way to do training or related work at a nearby military base, the official said.
"Apparently the police were looking for some bad guys and they ran into each other," said the official, who agreed to discuss the incident only if not quoted by name. "It looks like it was just a bad mistake ... they just shot and kept shooting."
The Navy said the embassy personnel were heading down a dirt road to the military installation when a carload of gunmen opened fire on them and chased them and a Navy officer accompanying them. The shooting broke out in an area that has been used by common criminals, drug gangs and leftist rebels in the past.
The Americans' vehicle tried to escape, but three other cars joined the original vehicle in pursuing them down the road, the statement said. Occupants of all four vehicles fired, and the Navy captain called more help, it said. Federal police officers and Mexican soldiers then showed up on the road, the statement said.
The U.S. vehicle appeared to be armored and it had diplomatic plates.
The Mexican government official said the wounded were not agents of the Drug Enforcement Administration or FBI, but did not identify which agency they work for.
"We are working with Mexican authorities to investigate an incident this morning in which two employees of our Embassy in Mexico City came under attack by unknown assailants. They are receiving appropriate medical care and are in stable condition. We have no further information to share at this time," said Victoria Nuland, a State Department spokeswoman in Washington.
The Mexican naval captain in the vehicle was not injured.
The vehicle was riddled with bullets, most concentrated around the passenger-side window.
The scene of the shooting, near the city of Cuernavaca, was cordoned off and guarded by more than 100 heavily armed marines and soldiers, and the highway was closed. Investigators examined what appeared to be shell casings.
U.S. Rep. Henry Cuellar, a Democrat from Texas who closely follows the affairs with Mexico, said both countries appeared to be working together to find out what went wrong.
"If the Mexicans are cooperating with U.S. officials to find out exactly what happened here then I don't think this will affect the U.S.-Mexico relationship," he said.
Attacks on diplomatic personnel in Mexico were once considered rare, but this was the third shooting incident in two years.
In 2011, a U.S. Immigration and Customs Enforcement agent was killed and another wounded in a drug gang shooting in northern Mexico.
A drug-gang shooting In 2010 in the border city of Ciudad Juarez killed a U.S. consulate employee, her husband and another man.
While Mexico City has largely been spared the drug violence that hits other parts of the country, Cuernavaca has been the scene of drug gang turf battles involving remnants of the Beltran Leyva cartel.