A US border agent "performing bike patrol duties" shot and killed a 14-year-old Mexican boy for throwing rocks at him on a bridge between El Paso and Ciudad Juarez on Monday. The boy's parents say he was in Mexico.

Officials in Juarez said the boy and his friends were playing on the Puente Negro bridge when they accidentally strayed into the US. At some point, rocks were thrown at agents, one of whom decided to open fire, killing a teenage boy. According to AFP:

Jesus Hernandez, the father, told W Radio his son went to the bridge to have lunch with his brother, who works nearby. At one point, "he went to the river bank to look to the other side.

"There were lots of kids and the border patrol cop... started firing off shots and hit my son, my baby twice in the head."

Hernandez said Mexican authorities had yet to contact the family about the incident.

The US State Department said US agents responded to "a group of suspected illegal immigrants from Mexico."

The FBI is investigating the killing and the border agent has been put on administrative leave. The Mexican Foreign Ministry issued a statement, saying, "The use of firearms to repel attacks with stones represents a disproportionate use of force." The boy's parents said he was shot and killed in Mexican territory.