The head of Israel's domestic security service issued a rare warning on Saturday of possible violence during one of the most politically charged periods in decades, with the country on the verge of unseating Prime Minister Benjamin Netanyahu, its longest-serving leader.

Netanyahu is facing the prospect of an end to his 12-year run as premier after Israel's centrist opposition leader Yair Lapid announced on Wednesday that he had succeeded in forming a governing coalition following a March 23 election...