CHISINAU (Reuters) - A no-confidence vote brought down Moldova’s government on Tuesday, threatening more instability just five months after pro-Western Prime Minister Maia Sandu took office promising to fight corruption.

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Sandu had formed an uneasy coalition with the Russian-backed Socialist Party, but relations broke down over a proposed reform of how the top prosecutor is appointed.

“We will continue the struggle, we will not give up,” Sandu told hundreds of supporters gathered outside parliament. “The struggle is between those who want to control justice and the prosecutor, and those who want freedom and fair justice.”

Moldova, a country of 3.5 million situated between Ukraine and European Union member Romania, has lurched from crisis to crisis since the disappearance of $1 billion from its financial system in 2014 tarnished the reputation of its political class.

The former Soviet state signed a political and trade agreement with the EU in 2014, angering Russia. Brussels and the International Monetary Fund support Chisinau with aid.

EU Commissioner Johannes Hahn tweeted he was “deeply worried” about Tuesday’s vote against Sandu. “Any change to her resolute action to reform the country over the last 5 months would have severe consequences on #EUsupport.”

Parties now have 90 days to try to form a new government. If they fail, another parliamentary election would be called.

Sandu, a Harvard-educated former World Bank economist known for her tough stance on corruption, had formed an unlikely alliance with the Socialists to remove a party run by a tycoon from power after an inconclusive election in February.

Sandu’s ACUM bloc wants Moldova to join the EU while the Socialist Party formerly run by President Igor Dodon advocates closer ties to Moscow.

After the vote, Dodon blamed Sandu for the row and called on the Socialists and ACUM to propose a new candidate for prime minister. He said the Socialists would try to run a minority government if the two sides could not compromise.

The coalition has tussled over who should have the power to appoint a new prosecutor general. Sandu wanted to be able to make the choice herself, but the Socialists wanted a special commission under the justice ministry to decide.

Sandu says the move is essential for her to be able to deliver on a promise to fight corruption and claw back the $1 billion that was stolen from three banks in a scam known locally as the “theft of the century”.