Mexican federal police who ambushed a US Embassy vehicle, wounding two CIA officers, were not investigating a kidnapping in the area, the attorney general's office said Sunday, contradicting the official police explanation of the shooting.

The CIA officers were heading down a dirt road to a military installation south of Mexico City on Aug 24 with a Mexican navy captain when a carload of gunmen opened fire on their SUV with diplomatic plates and gave chase. More vehicles joined in the pursuit, and the armored SUV was riddled with bullets.

The two CIA officers, who have not been identified, received non-life threatening injuries. The captain was not injured.

Mexican federal police maintain it was a case of mistaken identity since the officers were investigating a kidnapping of a government official in the area. Police suggested the officers might not have noticed the vehicle's diplomatic plates and thought they were shooting at criminals.

But on Sunday assistant prosecutor Victoria Pacheco Jimenez said the federal officers charged with attempted murder in the case were not working on a kidnapping at the time.

Pacheco said there was a kidnapping but "objectively it is unrelated to the investigation."

She said the investigation has shown that it was a direct attack on the US Embassy vehicle carried out by 14 federal police officers, all of whom have been detained.

Arrest orders were issued for four commanding officers for allegedly planning the attack and ordering agents to lie, but they have sought legal protections and remain free. A fifth commanding officer accused of covering up evidence has given his declaration to a judge and been released on bail.

All the gunfire came from the gunmen, discounting versions that the embassy vehicle fired first. The bullet-proofed SUV was struck by 152 bullets, 40 percent reaching the driver and passenger-side windows after the vehicle had come to a stop.

Pacheco didn't give a reason for the attack.

US and Mexican officials have told The Associated Press that evidence points toward an intentional attack, perhaps ordered by a drug cartel.

A senior US official has said there was strong circumstantial evidence that the officers were working for organized crime in a targeted assassination attempt. He spoke on condition of anonymity.

The rural road where the attack took place near Cuernavaca is known territory of the remnants of the Beltran Leyva gang. The once-powerful cartel has been run by Hector Beltran Leyva since Mexican marines killed his brother, drug lord Arturo Beltran Leyva, in Cuernavaca in late 2009.

Prosecutors say the police officers were dressed as civilians and were in private cars at the time of the attacks.

Asked if the attack involved organized crime, Pacheco said: "The assistant attorney general's office in charge of the case does not have that line of investigation."

Federal police spokesman Jose Ramon Salinas said Sunday he had no comment.

Federal police commissioner Maribel Cervantes earlier told the Mexican newspaper Milenio that she had spoken to US authorities and assured them that it was not an ambush or an attack, and had presented them with documentation backing the explanation that the officers were investigating a kidnapping.

The detained police face charges of attempted homicide, damage to property, carrying restricted weapons and covering up evidence.