Pro-Palestinian hackers disrupted Israeli websites on Tuesday, following threats from the Anonymous hacking collective that it would carry out an "electronic Holocaust," though Israeli cyber experts said the coordinated attacks caused little damage.

The hacking campaign, which has taken place every April 7 since 2013, is meant to be in protest of Israeli policies toward the Palestinians. In 2013, the hackers first waged the coordinated campaign, dubbed OpIsrael, on the eve of Israel's annual Holocaust remembrance day.

Israel's Computer Emergency Response Team, a civilian cyber security group, said Anonymous attacked a few dozen websites belonging to Israeli musicians and non-profit organizations on Tuesday. Anonymous had vowed it would topple Israeli government websites, banks and public institutions, though no major disruptions were reported.

The hackers replaced website home pages with photos of a Muslim holy site in Jerusalem and of militants holding the Islamic State militant flag, and posted a message signed by "AnonGhost."

"We are always here to punish you! Because we are the voice of Palestine and we will not remain silent!" the message read.

A video message by Anonymous said its campaign was responding to "crimes in the Palestinian territories," including last summer's Gaza war.

Israel's national cyber bureau said it distributed instructions to "relevant authorities" about boosting defense for websites ahead of the planned attack.