ST. LOUIS - An electric utility has asked a federal court in Illinois to toss out a lawsuit filed by a woman whose teenage son was seriously injured after he was shocked and tumbled 35 feet from an electric tower.

St. Louis-based Ameren Corp., which filed the court papers last week, insists the company and its Illinois subsidiaries "owed no duty" to protect trespassers such as Justin Porter, who climbed the tower in 2005 on a $5 bet. They said the boy should have known he was flirting with danger.

Porter's mother, Anna Thebeau, filed the lawsuit in April, accusing Ameren of "failing to exercise the highest degree of care" by affixing warnings to the tower and keeping youngsters from it when Porter, then 13, was zapped by a 19,700-volt power line at a tower near Mitchell, Ill.

Porter, of the St. Louis suburb of Granite City, Ill., survived. But the lawsuit says the boy suffered "serious personal injuries," including disfiguring second- and third-degree burns over 34 percent of his body, a fractured pelvis and tailbone, lacerated spleen and a bruised heart.

Thebeau first filed the lawsuit in Madison County, Ill., before Ameren moved the case to U.S. District Court in nearby East St. Louis, Ill.

The lawsuit seeks at least $100,000 in damages and compensation for $239,754 in medical expenses and $3,420 his mother claims she lost in wages taking her son to treatment. In its response filed last week, Ameren said Thebeau demanded $855,000 to settle the case April 17, five days after the lawsuit was filed.

Ameren and its subsidiaries say "the tower and electric lines were open and obvious, and constituted an obvious danger, to which no warning or other precautions were required."

"Plaintiff Justin Porter's negligence contributed in whole or in part to his injuries," Ameren's filing read.

In its request for dismissal, Ameren argues that in Illinois, "the general rule is that owners and occupiers of land are under no duty to trespassers to keep their premises in any particular state or condition to promote the safety of trespassers, whether they be minors or adults."

Ameren said courts elsewhere have held that utilities were not obligated to protect trespassers, citing the case of a 13-year-old mentally challenged boy shocked after climbing a ladder to reach a building's roof. A court later dismissed that boy's lawsuit, ruling the child was capable of appreciating the danger posed by electric lines.

Thebeau's lawsuit claims, without elaborating, that another child was "electrocuted" at the same tower - published reports say that happened three decades ago - and that Ameren "took no action in response" to keep children from frequently scaling the tower.

Messages left Monday by The Associated Press for Steve Evans, Thebeau's attorney, were not immediately returned.