Jojo Kalin, one of the event's organisers in Washington DC, told the BBC that the event the victims attended was focused on how to build a coalition to help people suffering in Gaza amid the ongoing Israel-Hamas war.
She added it is "deeply ironic that what we were discussing was bridge building and then we were all hit over the head with such hatred".
The attack was condemned by world leaders, including UK Prime Minister Keir Starmer, who said he "thoroughly" condemns the "antisemitic attack" in Washington DC.
Israeli Prime Minister Benjamin Netanyahu called the attack "a heinous antisemitic murder" and added that security would be increased for Israeli representatives and diplomatic missions worldwide.
US President Donald Trump also decried antisemitism in response to the attack, writing on his social media platform Truth Social that "hatred and radicalism have no place in the USA."
Trump and Netanyahu later spoke over the phone about the incident, where the US president expressed sorrow to his Israeli counterpart, according to a readout of the call.
