Robert Serry, the UN Special Coordinator for the Middle East Peace Process, issued a statement at the weekend in which he said he was appalled by last Friday morning's attack on the mosque in the village of Yassuf.
Media reports say the mosque was set ablaze and vandalized, with hate messages scrawled in Hebrew and holy books burned or singed.
"Desecrating a place of worship is deplorable," Mr. Serry said. "This attack is a part of a broader and ongoing phenomenon of settler violence against Palestinian civilians, property and land.
"Far too little is done by the Israeli authorities to enforce the rule of law on violent extremists, leading to a climate of impunity. We hope and expect that the authorities will seek out those responsible for this latest incident, along with other acts of violence and bring them to justice."
Senior UN officials have in recent weeks called for a halt to Israeli settlement activity and have also voiced concern about the demolition of Palestinian homes and evictions in East Jerusalem.