STUTTGART, Germany (Reuters) - German left-wing demonstrators clashed with police on Saturday as they tried to break up the first full conference of the anti-immigration party Alternative for Germany where Chancellor Angela Merkel’s policies came under attack.

Police counted up to 2,000 left-wing protesters, some of whom burned tires and hurled stones and fireworks to try to stop the AfD’s congress going ahead in Stuttgart. Some 500 were detained, police said.

Two policemen were slightly injured, but there were no reports of injured among the protesters, police spokesman Lambert Maute said.

Buoyed by the migrant crisis, which saw the arrival of more than one million migrants in Germany last year, the AfD has upended German party politics.

After the congress started late, more than 2,000 AfD members listened to their party leaders’ call for an end to Merkel’s refugee-friendly politics and a return to Christian values.

“We always wondered when the brave child will finally appear to voice the thoughts of the silent majority and declare that the ‘Chancellor of no alternatives’ is nothing but naked,” said party leader Frauke Petry, 40, in her opening speech.

“And I think, this brave child is us,” Petry added.

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The violence began around dawn and clashes continued for several hours. Police used pepper spray and threatened to use water cannons to stop protesters, some of whom were masked, from getting onto the grounds of the conference. Some demonstrators still managed to assault several party members, they said.

The AfD has mainly run on an anti-migrant and Islam-critical agenda, but now struggles to unite its various fractions under one party program that could put it on a broader footing.

It currently has representatives in half of Germany’s sixteen federal state parliaments and the party has its eyes set on next year’s federal elections.

Opinion polls see the party coming in at between 10 and 14 percent, a serious challenge to established party politics, though these have ruled out forming any coalition with the AfD.

The AfD however considers itself in good company on a European level, following election gains by far-right parties across the continent.

Petry used her oratorical skills to denounce what she termed the hypocrisy of the ruling elite whose policies, she said, were directed against the interest of ordinary German citizens.