A right-wing challenge to Prime Minister Benjamin Netanyahu in a March Israeli election gained momentum on Wednesday with the defection of a long-time ally to an upstart rival party.

In a letter announcing his resignation from Netanyahu's right-wing Likud party and parliament, Zeev Elkin, a minister in successive Netanyahu governments, accused Israel's longest-serving prime minister of putting his own interests ahead of those of the country.

"I can't ask Israelis to vote for you (Netanyahu) and to be satisfied that you are not putting your personal interests ahead of theirs," Elkin said in a speech broadcast live by Israeli television channels.

The election will be Israel's fourth in two years, and comes as Netanyahu faces criticism over his handling of the COVID-19 pandemic and battles corruption allegations, which he denies.

Elkin will join a new party led by fellow former Likud legislator Gideon Saar, who earlier this month announced a breakaway bid aimed at defeating Netanyahu. Saar announced Elkin's move to his party in a tweet, though Elkin made no mention of it in his speech.

The defections pose a new challenge to Netanyahu ahead of a March 23 snap election. Parliament's failure to pass a national budget on Tuesday triggered the early ballot.

Until his resignation, Elkin served as Israel's minister of higher education and water resources. Born in Ukraine, Elkin is fluent in Russian and has long served as Netanyahu's interpreter and adviser in strategic talks with Russian President Vladimir Putin.

Earlier on Wednesday, Sharren Haskel, a junior Likud lawmaker, also announced she was defecting to Saar's new party, writing in a Facebook post that Netanyahu's government "has lost the moral mandate to continue to govern."