A man accused of using a makeshift flamethrower and an incendiary device to attack a group in Boulder, Colorado, that had gathered to bring attention to Israeli hostages in Gaza, has been charged with a federal hate crime, according to court documents.

The suspect, Mohamed Sabry Soliman, was charged in the attack that injured eight people, some with burns, as a group was concluding their weekly demonstration to raise visibility for the hostages who remain in Gaza.

Authorities say Soliman yelled "Free Palestine" during the attack in the US city on Sunday, the beginning of the Jewish holiday of Shavuot.

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It came barely a week after a man who also yelled "Free Palestine" was charged with fatally shooting two Israeli embassy staffers outside of a Jewish museum in Washington.

FBI leaders immediately declared the attack an act of terrorism and the Justice Department denounced it as a "needless act of violence, which follows recent attacks against Jewish Americans".

More to come.