Jewish settlers or their supporters were suspected of setting a mosque in an Arab village in northern Israel on fire.
Graffiti on the walls pointed to settler involvement, said police spokesman Micky Rosenfeld.
He said a carpet was burned and interior walls damaged at the mosque in Tuba-Zangria in the Galilee region. Israel Radio also reported that Korans were burned.
Mr Rosenfeld said the words "price tag" were spray painted on the building - a reference to a settler practice of attacking Palestinians and their property in retaliation for government operations against settlements.
Several weeks ago the government destroyed unauthorised structures in an illegal settlement outpost in the West Bank - an operation that was followed immediately by another mosque blaze.