WASHINGTON, March 27 (Xinhua) -- Three children and three adults died after a shooting at an elementary school in Nashville, the U.S. state of Tennessee, on Monday.

The mass shooting was reported at the Covenant School, a private Christian elementary school in Nashville, on Monday morning.

Don Aaron of the Metro Nashville Police Department (MNPD) told reporters that the students were fatally wounded and that three adult staff members who were shot are also deceased.

Aaron said the shooter was a female and armed with at least two "assault-type" rifles and a handgun, and that she was shot dead by police during their encounter.

"Two MNPD officers who entered the building and went to the sounds of gunfire engaged the shooter on the second floor and fatally shot her," the MNPD tweeted on Monday afternoon.

Police haven't identified the shooter but said she was a 28-year-old woman. It remains unclear whether the shooter had any connection to the grade school.

U.S. first lady Jill Biden said on Monday afternoon that she's "truly without words" after learning about the Nashville school shooting.

"Our children deserve better. And we stand, all of us, we stand with Nashville in prayer," she said from an event in Washington, D.C.

There have been 128 mass shootings in the United States so far this year, according to the Gun Violence Archive, which defines a mass shooting as one in which at least four people are shot, excluding the shooter.

Meanwhile, more than 9,800 people, including hundreds of children and teens, have lost their lives to gun violence in the past three months, the website's data showed.

White House press secretary Karine Jean-Pierre said at the daily briefing on Monday that "we need to do something."

Jean-Pierre told reporters that U.S. President Joe Biden once again "calls on Congress to do something before another child is senselessly killed in a preventable act of gun violence."

The Covenant School serves about 200 students from preschool through 6th grade, according to its website.