All six of those hit were taken to hospitals, where three died, Contee said.
He said the slain all appeared to be young adults.
The other three were also adults, but no ages were given. Police described their wounds as not life-threatening.
The assailants fired into a group of people, and at least some in the group were apparently targeted, the chief said.
He did not say why they might have been targeted.
A weapon was found at the scene, Contee said, adding that police were trying to determine whether it had any role in the gunfire.
No names were released immediately for those who were killed. Contee said police were still trying to notify their relatives.
The triple slaying raised the number of homicides in the city this year to at least 144, an increase of about 15 percent over last year at this time.
Even with the surge, a shooting with three fatalities is unusual in Washington.
The shooting was in a neighborhood where residents last year expressed concern about what they described as an increase in gun violence.
Shootings involving illegal firearms have become “a sickness” throughout the nation and in the District, Contee said. He called on members of the community to help find those responsible for Saturday evening’s gunfire.
Two neighbors reported
hearing the shots from inside their houses on Saturday.
One said she first thought she was hearing fireworks. There were many bangs, she said, speaking on the condition of anonymity out of concern for her privacy. “It was a lot.”
Then, she said, she opened her door to see the police arrive and thought, “Oh, it was not fireworks.”