GREAT MILLS, Md. (AP) — The Latest on the shooting at a Maryland high school (all times local):

10:45 a.m.

The principal at the Maryland high school where there was a shooting Tuesday morning told parents last month that the school had investigated threats of a possible shooting and found they were "not substantiated."

Great Mills High School Principal Jake Heibel told parents that school officials interviewed two students in February who were overheard mentioning a school shooting and found that they posed no threat. His letter was posted on the local news site The Bay Net.

But Heibel said the school still increased its security after social media posts about a possible school shooting "circulated quite extensively."

St. Mary's County Sheriff's spokeswoman Cpl. Julie Yingling says three people, including the shooter, were injured in Tuesday's shooting.

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10:15 a.m.

A sheriff's spokeswoman says three people have been injured in a shooting at a high school in southern Maryland, including the shooter.

St. Mary's County Sheriff's spokeswoman Cpl. Julie Yingling says there have been no fatalities in the Tuesday morning shooting at Great Mills High School.

Yingling says the two victims were shot, but she doesn't know how the shooter was injured. She also didn't have the identities of the any of the three injured.

She says all three had been transported to hospitals.

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Update: 10:29 a.m.:

A shooting at a Maryland high school Tuesday morning injured three people, including the shooter, a sheriff's spokeswoman said.

Authorities said the situation was "contained" as deputies and federal agents converged on the crime scene.

St. Mary's County Sheriff spokeswoman Cpl. Julie Yingling said three people hurt, including the shooter. She didn't know the extent of their injuries, but said all three were taken to hospitals and none were killed.

The Baltimore Sun reported that a student said the shooting happened around 8 a.m. Terrence Rhames, 18, told the Sun that he heard a gunshot and saw a girl fall as he ran for an exit. "I just thank god I'm safe," Rhames said. "I just want to know who did it and who got injured."

The St. Mary's County Public Schools said the situation was "contained" after the shooting at Great Mills High School, which has about 1,600 students and is near the Patuxent River Naval Air Station, about 65 miles (104 kilometers) southeast of Washington.

Agents with the FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives joined deputies at the scene. The county sheriff said parents or guardians should stay away, urging them to go instead to Leonardtown High School to reunite with Great Mills students there.

Maryland Gov. Larry Hogan and Rep. Steny Hoyer tweeted that they're monitoring reports and urged people to follow the instructions of local law enforcement at the scene.

This latest shooting happened as many students are calling for action against gun violence in schools, leading up to Saturday's March For Our Lives rally in the nation's capital. Protests have been spreading around the nation since a teenager with an assault rifle killed 17 people at a Florida high school on Valentine's Day. Threats against schools have proliferated as well.

Last month, the St. Mary's County Sheriff's office said it arrested two teenage boys for "Threats of Mass Violence" and a 39-year-old man on related charges after the teens made threats about a potential school shooting at nearby Leonardtown High. Police said they obtained search warrants and found a cache of semi-automatic rifles, handguns and other weapons.

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GREAT MILLS, Md. (AP) — School officials report that there's been a shooting at a Maryland high school, that the 'event is contained' and the campus is on lockdown.

The St. Mary's County Public Schools said on its website early Tuesday that there was a shooting at Great Mills High School, located in the southern end of the state.

The office of the county sheriff said there was an "incident" at the school, and asked parents to stay away from the campus, reporting instead to Leonardtown High School instead.

The school is in the congressional district of Rep. Steny Hoyer, who tweeted that he's closely monitoring reports and urged people to follow the instructions of local law enforcement at the scene.