President Donald Trump quickly condemned the attack.
According to AFP, gunfire broke out on the sidewalk outside the Capital Jewish Museum in the center of Washington as the venue held a social event for young professionals and diplomatic staff.
The victims were a young couple who planned to get married, the Israeli ambassador said.
A video clip circulating on social media showed a young bearded man in a jacket and white shirt shouting "free, free Palestine" as he was led away by police.
Police confirmed the suspected shooter walked into the museum after the shooting and had been detained.
"We believe the shooting was committed by a single suspect who is now in custody," Washington Police Chief Pamela Smith told reporters.
"Prior to the shooting the suspect was observed pacing back and forth outside of the museum. He approached a group of four people, produced a handgun and opened fire.
"After the shooting, the suspect then entered the museum and was detained by event security."
She said the handcuffed suspect identified where he had discarded the weapon and chanted "Free, free Palestine."
Police identified him as Elias Rodriguez, 30, from Chicago.
"I am devastated by the scenes in Washington," Israeli regime's head Isaac Herzog said in a statement.
MNA
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