CIUDAD JUAREZ, Mexico (Reuters) - A Mexican mother whose teenage son, Sergio Adrian Hernandez Guereca, was shot dead by a U.S. Border Patrol agent from the other side of the border 10 years ago fears a U.S. Supreme Court ruling on Tuesday that barred her lawsuit could endanger others.

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Earlier, the court ruled 5-4 to uphold a lower court’s dismissal of the lawsuit against the agent, Jesus Mesa, who stood on the U.S. side when he shot across the border into the face of the 15-year-old.

Standing in a culvert right on the Mexican side of the border, clutching her son’s framed photograph, Maria Guadalupe Guereca said the ruling could embolden other U.S. Border Patrol agents.

“They’ll feel that they have the right to kill innocent people, that they can continue killing children,” said Guereca, adding that her son had never caused her trouble.

“He was just a boy,” she said, in tears.

Mesa did not face criminal charges. U.S. Border Patrol has said the teenager had pelted its agents with rocks from the Mexican side.

The FBI accused him of being a migrant smuggler.

Lawyers who represented the family said he was simply playing a game in which a group of teenagers would run across the culvert from the Mexican side and touch the U.S. border fence before running back.

Issued at a time of high tension between both countries, the ruling prevents civil rights lawsuits in U.S. federal courts involving such cross-border incidents when the person who is injured or killed is not on U.S. soil.

Later on Tuesday, the Mexican government said it is deeply concerned about the effects the decision would have on similar cases in which its citizens have died from gunshots fired by U.S. agents towards the Mexican side.

“I ask that they analyse the case,” said Guereca, who vowed to keep fighting for justice even as legal experts said she had run out of options.

“It’s not fair what they have done.”