Israeli Defence Minister Moshe Yaalon resigned Friday, citing a "lack of faith" in Prime Minister Benjamin Netanyahu amid a reshuffle in the cabinet.
Netanyahu, from the right-wing Likud party, has been moving to replace Yaalon with hardliner Avigdor Lieberman, a former foreign minister.
The move is meant to expand his coalition, comprised already of several parties but which has only a one-seat majority in the legislature.
Lieberman, a nationalist populist, is the leader of the hawkish Israel Beiteinu party, which has six members in the Knesset.
He has relatively little military experience. Most defence ministers in Israel have extensive backgrounds in the army, often serving as generals.
"To my great regret, extremist and dangerous elements have taken over in Israel, and also over the Likud movement," Yaalon said, adding that he would take a break from politics and resign from the Knesset.
He vowed to return in the future to contend for a leadership post.Yaalon, is due to be replaced in parliament by Yehuda Glick, a religious settler who lives on the occupied West Bank and has stirred up tensions over holy sites in Jerusalem.
Yaalon is a former Israeli chief of staff in the army and has been defence minister for the past three years.
Israel held elections in March last year, returning Netanyahu to the premiership, a job he has held since 2009. He was also prime minister for three years in the 1990s.
Peace talks between Israel and the Palestinians have long since been frozen but additional hardliners in the government would make any chance of reviving them more remote.