Ettinger, a grandson of Meir Kahane, a rabbi who founded the racist anti-Arab movement Kach and was assassinated in 1990, was arrested in Safed in northern Israel "because of his activities in a Jewish extremist organisation", a spokesman for the domestic intelligence service Shin Bet told AFP.
A police spokeswoman said Ettinger, who is aged around 20, was suspected of "nationalist crimes" but did not accuse him of direct involvement in Friday's firebombing.