Mexico City (AFP) - Mexican police wounded a pregnant US teenager when they opened fire on a vehicle that ignored orders to stop, authorities said Monday, in the latest episode of violence involving Mexico's security forces.

Both the girl and the baby are out of danger, said prosecutors in the violence-plagued northeastern state of Tamaulipas, which borders the United States.

The girl and a friend were leaving a convenience store Sunday night near a bridge that links the Mexican border city of Reynosa and Pharr, Texas, when state police officers ordered their truck to stop.

Instead the driver sped away and police shot at the tires, the prosecutor's office said in a statement.

When police reached the truck, the driver had disappeared and the girl was found with a stomach wound. The officers took her to a hospital.

The statement said an unspecified number of officers will be questioned over the shooting.

Mexico's security forces have been involved in a series of scandals recently.

In Tamaulipas, three American siblings and a Mexican men were found dead on October 30, two weeks after they were abducted outside the border city of Matamoros.

Prosecutors investigating the murder have questioned nine agents from the tactical Hercules Group tasked with protecting the mayor after the families of the victims alleged that they had kidnapped the siblings.

In the southern state of Guerrero, authorities have arrested 36 municipal police officers over charges that they shot at busloads of college students and handed 43 of them to a drug gang.

Authorities said last week that suspected Guerreros Unidos gang members confessed to killing the students and incinerating their bodies in a crime that has rocked President Enrique Pena Nieto's administration.

The government is also dealing with allegations of military abuse after seven soldiers were arrested in connection with the killing of 22 gang suspects south of Mexico City.

Prosecutors have charged three of the seven with murder over the deaths of eight suspects, but the National Human Rights Commission says at least 12 suspects were killed after surrendering following a shootout.