Israeli Defence Minister Avigdor Lieberman announced his resignation on Wednesday and called for early elections after a sharp disagreement over a Gaza ceasefire deal.
He also said his party was quitting Prime Minister Benjamin Netanyahu's coalition, leaving the premier with only a one-seat majority in parliament.
Lieberman heads the right-wing Yisrael Beitenu party,
which holds five seats in the 120-seat Knesset, or parliament.
Elections are not due until November 2019, but Lieberman's resignation increases the likelihood of an earlier vote.
Meanwhile, Mr Netanyahu has defended yesterday's ceasefire deal that ended the worst escalation between Israel and Palestinian militants in Gaza since a 2014 war.