A vigil was held in Nashville, the capital of the U.S. state of Tennessee, on Wednesday for the three children and three adults shot to death during Monday's massacre at a private Christian school.

The victims' names were repeatedly recited during the tribute – 9-year-old students Evelyn Dieckhaus, William Kinney and Hallie Scruggs, along with custodian Mike Hill, 61, the school's headmaster Katherine Koonce, 60, and substitute teacher Cynthia Peak, 61.

"Nashville has had its worst day. Our hearts are broken," said Mayor John Cooper, accompanied by numerous local leaders and clergy. 

The perpetrator of Monday's carnage, former Covenant School student Audrey Elizabeth Hale, 28, was fatally shot by responding officers.

While Hale targeted the school – housed in the Covenant Presbyterian Church and serving about 200 students from pre-kindergarten to sixth grade – the individual victims were slain at random, police have said.

Authorities have yet to pinpoint the motive, according to Nashville police chief John Drake, adding that investigators are also looking at the mental health of the shooter, who was under a doctor's care for an emotional disorder.

Monday's shooting was the latest of dozens in U.S. schools this year. As with most high-profile mass shootings, the latest attack has added fuel to a long-running national debate over gun ownership rights and regulations.

U.S. President Joe Biden said from an event in Durham, North Carolina, on Tuesday that "as a nation, we owe these families more than our prayers."

"We have to do more to stop this gun violence from ripping communities apart, ripping apart the soul of this nation, to protect our children, so they learn how to read and write instead of duck and cover in a classroom," Biden said.

He also reiterated his call for U.S. lawmakers to pass an assault weapons ban, stating that there was a "moral price to pay for inaction."

(With input from agencies)