The family of a Mexican man who they say was killed by a Border Patrol agent's shot across the Rio Grande has sued the U.S. government.

The lawsuit filed in federal court in Brownsville on Friday alleges the agent used unlawful force in shooting 30-year-old Juan Pablo Perez Santillan.

Border Patrol says illegal immigrants were throwing rocks at agents while they detained a group that had crossed the river July 7. Another agent fired across the river when someone was seen aiming a rifle.

The Mexican government has confirmed that Perez Santillan was killed on the river bank in Matamoros. His family says in the lawsuit that he was unarmed and signaling groups when to cross the river.

A Border Patrol spokesman declined to comment on the lawsuit Tuesday.