Police in New Orleans were searching for at least two gunmen after at least 19 people, including two children, were wounded when shots were fired at a Mother’s Day parade
Police said many of the victims were grazed, and most of the wounds were not life-threatening.
FBI spokeswoman Mary Beth Romig said investigators had no indication that the shooting was an act of terrorism.
"It's strictly an act of street violence in New Orleans," she said. The southern city has one of the highest violent crime rates in the US.
A news release said the wounded included two 10-year-olds. It also said two people were undergoing surgery.
Police saw three suspects running from the scene. No arrests have been made.
As many as 400 people joined what is known as a second-line parade, a loose procession in which people dance down the street, often following a brass band. They can be impromptu or planned.
Officers were interspersed with the marchers, which is routine for such events.
The neighbourhood where the shooting happened was a mix of low-income and middle-class row houses, some boarded up. As of last year, the neighbourhood's population was about 60% of its level before Hurricane Katrina devastated New Orleans in 2005.
Police vowed to make swift arrests.
"We'll get them. We have good resources in this neighbourhood," police superintendent Ronal Serpas said.