Israeli Defence Minister Moshe Yaalon has resigned, warning that Israel has been taken over by “dangerous and extreme elements”.
It comes as Prime Minister Benjamin Netanyahu seeks to bring hardliner Avigdor Lieberman into the coalition, possibly as defence minister.
The deal would shore up Mr Netanyahu’s one-seat majority in parliament.
Mr Lieberman has a reputation for inflammatory comments and takes a hawkish stand towards the Palestinians.
If his six-seat Yisrael Beiteinu party joins the coalition, it will become the most right-wing in Israel’s history.
Announcing his decision on Twitter, Mr Yaalon said: “I informed the PM that after his conduct and recent developments, and given the lack of faith in him, I am resigning from the government and parliament and taking a break from political life.”
The two men had publicly disagreed after Mr Yaalon backed a senior military figure who had made controversial remarks about perceived extremist trends in Israeli society on Holocaust Day earlier this month.