Israel’s Defense Minister Moshe Yaalon announced his resignation on Friday, citing poor faith in Prime Minister Benjamin Netanyahu who allegedly offered his post to hardliner Avigdor Lieberman.

“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,” Yaalon said on Twitter.

Political sources say Netanyahu offered ultra-nationalist politician Lieberman on Wednesday the defense portfolio as part of a move to expand the coalition government.

The portfolio is a post crucial for a country on a perennial war footing and which also runs civil affairs in the occupied West Bank, where Palestinians struggling for statehood live in friction with Jewish settlers.

Yaalon’s exit could put a new dent in domestic and Western confidence in the Netanyahu government.

A former chief of Israel’s armed forces, Yaalon had shored up ties with the Pentagon that provided a counter-weight to Netanyahu’s policy feuds with U.S. President Barack Obama over peace talks with the Palestinians and Iran’s nuclear program.

By contrast, Lieberman – whose appointment has not been confirmed – is inexperienced militarily and known for his past hawkish talk against Palestinians, Israel’s Arab minority and Egypt – a key regional security partner for Israel.

Lieberman, 57, is also one of the country’s most polarizing politicians. Over three decades, he has at times been the prime minister’s closest ally and other times a fierce rival.

This week, Netanyahu invited Lieberman’s party Yisrael Beitenu to join his narrow coalition. The inclusion of the party in the coalition, which has yet to be confirmed, would give Netanyahu’s Likud party control over 67 of parliament’s 120 seats, up from the current razor-thin majority of 61.

The prime minister’s offer of Yaalon’s cabinet post to Lieberman emerged this week after talks on bringing center-left opposition leader Isaac Herzog into the government failed.