A 7-year-old boy in St. Louis was shot and killed on Monday, the 11th child in the area to die by gunfire since June.

Xavior Usanga was playing with siblings in front of his house Monday afternoon, just days before the start of the new school year, according to NBC St. Louis affiliate KSDK. An 18-year-old male was also injured in the shooting, the St. Louis Metropolitan Police Department said. Officials found a firearm at the scene but are still looking for the shooter.

"This little kid would have been starting school this week," St. Louis Metropolitan Police Chief John Hayden said at a press conference Monday, holding back tears. "It's just not right."

St. Louis Mayor Lyda Krewson tweeted on Tuesday that she was "sick and outraged."

"Yesterday 7 yr old was shot & killed while playing outside at 5pm. WHO does this! Who shoots towards a child- a 2nd grader. Many shots fired. Incomprehensible!" she wrote on Twitter, urging anyone with information about the shooter to come forward.

I’m sick & outraged! Yesterday 7 yr old was shot & killed while playing outside at 5pm. WHO does this! Who shoots towards a child- a 2nd grader. Many shots fired. Incomprehensible!



Feuding, fighting teens & adults- maybe retaliation. CrimeStoppers text 274637 call 866-371-8477 — Mayor Lyda Krewson (@LydaKrewson) August 13, 2019

St. Louis has consistently ranked among the most dangerous cities in America. In 2015, the FBI's Crime Report identified it as the most dangerous, with 1,817 violent crimes per 100,000 people.

But this summer has been particularly violent, especially for young children, experts said. Among the children who have died by gun violence is a 3-year-old who was shot in a drive-by shooting on June 9.

"It's not unusual for teenagers under the age of 18, let's say between 14 and 18, to be shot and killed, unfortunately. But for children under the age of 12 to be killed in the numbers that have occurred in the last year or so in St. Louis is unusual," said Richard Rosenfeld, a criminologist at the University of Missouri-St. Louis. "I don't think children are the targets in these cases."

Rosenfeld added that St. Louis has "the conditions that give rise to high levels of firearm violence that every other city with a firearm violence problem has, but to a more extreme degree." Among the factors he cited: racial segregation, high levels of joblessness and poverty, and many drug-related incidents of violence.

The St. Louis Metropolitan Police Department did not immediately return an inquiry from NBC News about how many youth were fatally shot in prior summers. Rosenfeld said he suspected that more young children were being shot this year because of "the greater use of automatic weapons and more rounds discharged at a target."

"If the target happens to be near a child, the child is more likely than in the past to be killed," he said.

Hayden, the police chief, has attributed many of St. Louis's recent homicides to drug-related activity. He asked the public to share any information that could lead to an arrest in Xavior's killing.

“This case should be solvable,” he said at Monday's press conference. “This can’t be, ‘I’m afraid to talk to the police.’ I’m hoping people will listen to my plea.”