Whether the setback to Mr. Berlusconi is only temporary will be seen in a May 29 runoff.

Premier Silvio Berlusconi and his coalition partners have suffered setbacks in local elections across their northern Italian powerbase.

Mr. Berlusconi’s candidate in his native Milan, the incumbent Mayor Letizia Moratti, will face a runoff against the centre—left candidate later this month. Final results from voting on Sunday and Monday showed Ms. Moratti trailed by six percentage points in a race that Mr. Berlusconi called a referendum on his government.

Whether the setback to Mr. Berlusconi is only temporary will be seen in a May 29 runoff.

Mr. Berlusconi’s candidate in Naples led the voting but failed to win a majority in a bid to take back the seat held by the centre—left. A runoff is necessary. The opposition centre—left won mayoral races outright in traditional strongholds Turin and Bologna.

Mr. Berlusconi’s coalition partners, the Northern League, lost support in 14 of 15 major contests.

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