By Stefano Rellandini
BOLOGNA, Italy (Reuters) - Italy's divided conservative parties joined forces for a rally in the northern town of Bologna on Sunday, promising to work together to oppose and oust center-left Prime Minister Matteo Renzi.
The rally was organized by the anti-immigrant Northern League party led by 42-year-old Matteo Salvini, which has eclipsed former Prime Minister Silvio Berlusconi's Forza Italia to emerge as the largest force on the right.
Berlusconi, 79, has kept a low profile since he was convicted of tax evasion and banned from public office in 2013, but he attended Sunday's rally along with Giorgia Meloni, the leader of the small, far-right Brothers of Italy party.
"With this newfound unity, staying together and fighting together, we will win the next elections," Berlusconi told tens of thousands of marchers crammed into Bologna's main square.
People waved Northern League, Forza Italia and Brothers of Italy flags and chanted slogans against Renzi and his government. "Go home, Renzi! Let's free ourselves, let's start again!" read one slogan.
In a blunt speech, Salvini took aim at targets ranging from Italy being too lax on immigrants, the government allowing multinationals to buy Italian firms and lay people off, to a lack of opportunities for the young.
Hundreds of police were deployed to keep order around Bologna's city center throughout the rally. Television pictures showed officers in riot gear charging hundreds of left-wing protesters who threw firecrackers and rudimentary paper bombs.
The center-right has often been divided since shortly after a 2013 parliamentary election. The League has maintained hardline opposition to the government while Berlusconi has wavered between modest opposition and collaboration with Renzi.
All Berlusconi's three election victories since 1994 were in alliance with the League, and the center-right parties have pledged to work together in parliament ahead of mayoral elections next year in Rome, Milan, Naples and Bologna.
Opinion polls give the Northern League around 14 percent of the vote, in third place behind Renzi's Democratic Party (PD), on around 31 percent, and the anti-establishment 5-Star Movement, on about 27 percent.
Forza Italia is polling at about 12 percent and the Brothers of Italy at 4.5 percent. If all three center-right parties join forces they could be a threat to the PD, which is the only major party on the center-left.
The next parliamentary election is due in 2018, but commentators speculate it could come earlier as a result of instability in Renzi's ruling coalition.
Renzi suffered a potential setback on Saturday when a group of former PD dissidents who quit the party complaining he had moved too far to the right, formed a new movement called Italian Left, which will hope to lure left-wing voters away from the PD.
(Writing by Gavin Jones and Agnieszka Flak; Editing by Janet Lawrence)