The Mexican Navy said the US personnel were on a main road to the city of Cuernavaca when the shooting happened.

Details are still unclear, but the navy said the US vehicle had been fleeing from gunmen in another car.

The US state department said it was working with Mexican authorities to investigate the incident.

Spokeswoman Victoria Nuland said the two men were receiving "appropriate medical care and are in stable condition".

"We have no further information to share at this time," she added.

One of the men was said to have been hit in the leg and the other in the stomach and hand. Both were admitted to hospital.

A Mexican marine travelling with the two US employees was slightly injured in the incident, the navy said.

The Mexican public security ministry and marines said in a joint statement: "Today at 08:00 a diplomatic vehicle belonging to the US embassy was hit by multiple bullets from personnel of the federal police in the Tres Marias-Huitzilac highway."

It said the embassy personnel had been heading to a military installation in the town of El Capulin when a carload of gunmen opened fire on them and chased them, along with the Mexican naval officer accompanying them.