Washington, Sep 6 (IANS): A 14-year-old boy has been charged with murder for shooting four people dead at a US high school, authorities said, adding that their investigation into the country's latest outburst of gun violence is ongoing.

The teen faces four felony murder counts after allegedly killing two fellow children, also aged 14, as well as two teachers at Apalachee High School in the southern state of Georgia on Wednesday.

Citing unnamed sources, CNN reported on Thursday that the gun used in the shooting -- which it described as an AR 15-style assault rifle -- had been purchased for the teenager by his father as a holiday gift.

The Georgia Bureau of Investigation had said the suspect identified as Colt Gray would be charged as an adult. It said that he would appear in court on Friday, and that additional charges are expected.

"The investigation into the shooting at Apalachee HS is still active and ongoing," the agency said on Thursday in a post on X.

"This is day 2 of a very complex investigation and the integrity of the case is paramount," it said, adding that all four victims would be autopsied on Thursday.

School shootings are a shockingly regular occurrence in the US, where guns outnumber people and regulations on purchasing even powerful military-style rifles are lax.

Parental responsibility in mass shootings, particularly by minors, has come increasingly under the spotlight in recent months.

"How could you have an assault rifle, a weapon in a house, not locked up and knowing your kid knows where it is?" lamented President Joe Biden, speaking to reporters in Wisconsin on Thursday.

"You've got to hold parents accountable if they let their child have access to these guns."

In April, the parents of a teenager who killed four people in a school shooting in Michigan were sentenced to 10 to 15 years in prison, in an unprecedented and closely watched case.

Jennifer Crumbley, 46, and her husband James, 47, were the first parents of a school shooter convicted of involuntary manslaughter in the US for the actions of their child.

Polls show a majority of voters favour stricter controls on the use and purchase of firearms, but a powerful gun ownership lobby is opposed to additional restrictions and lawmakers have repeatedly failed to act.