In a statement released by his spokesman, Mr. Annan said “such attacks underscore the destructive power that militants have to derail the crucial efforts under way to de-escalate tensions.”

Mr. Annan called on both sides “to adhere strictly to their commitment, and avoid hasty action which could jeopardize progress towards a sustained period of calm,” adding that he hoped Israel and the Palestinians will extend the ceasefire to the West Bank as well.

Israeli President Ehud Olmert and Palestinian President Mahmoud Abbas announced on Saturday that they had agreed to a ceasefire, which follows a month of intense violence in Gaza.