Story highlights Border Patrol says rocks were thrown at its agents

Mexico's foreign ministry criticizes "disproportionate use of lethal force"

The FBI is investigating

Mexico's foreign ministry has accused a U.S. Border Patrol agent of fatally shooting a Mexican citizen along the border.

The shooting occurred Monday after agents in the area of Laredo, Texas, "were subjected to rocks being thrown at them from the Mexican side of the Rio Grande River," the patrol's Laredo sector said Thursday.

"A weapon was discharged by Border Patrol. All appropriate authorities were notified and the shooting is under investigation by the Federal Bureau of Investigation," the statement said.

The U.S. statement did not specify whether a death occurred.

Mexico's foreign ministry said a Mexican national died after being shot by a U.S. agent between Laredo and Nuevo Laredo, Mexico. The ministry did not release details about the circumstances surrounding the Monday violence.

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"The Mexican government has repeatedly expressed that the disproportionate use of lethal force in the exercising of immigration control functions is unacceptable under any circumstance," the foreign ministry said Wednesday, calling for a thorough investigation.

The Mexican foreign ministry released a similar statement in July , after it said that a U.S. Border Patrol agent had killed a Mexican citizen near the bridge between Matamoros, Mexico, and Brownsville, Texas.

At the time, a U.S. Customs and Border Protection spokesman said two agents fired shots during "dangerous encounters" along the border.