A student fired a pellet gun in a courtyard during lunch at a high school Wednesday, leaving six boys with minor injuries, police said.

The boys, ages 14 to 16, reported hearing six popping sounds and then feeling a stinging sensation where they were struck by the pellets — on their chests, arms and legs. They were treated by the school nurse, and none was seriously injured.

The incident came after a string of violent shootings at high schools in Colorado and Wisconsin and at an Amish school in Pennsylvania.

Authorities later found the pellet gun under a bush on school grounds, said Sgt. Vickie Warehime, a spokeswoman for Baltimore County police.

Police said they believe it was a student because no one was seen entering Pikesville High. Three officers were at the school on an unrelated matter before the shootings.

Police planned to check the gun for fingerprints. Detectives were interviewing the victims' friends, other students and faculty for any leads on a possible suspect.

Elsewhere Wednesday, a middle school inJonesboro, Ark., was locked down temporarily after a teacher discovered that a student brought a Molotov cocktail into the building.

Police Capt. B.J. Smith said the 14-year-old student, who was being held at a juvenile detention center, had filled a bottle with gasoline and was carrying paper towels to use as a wick. The incident took place across town from another middle school where four girls and a teacher were killed by two boys, ages 11 and 13, firing from nearby woods in 1998.

Also Wednesday, more than a dozen schools in three Nebraska counties were locked down after someone called a local newspaper and said there would be a school shooting. There were no reports of violence, though some schools told parents to come and pick up their children.