Stuttgart (Germany) (AFP) - Germany's right-wing populist AfD Sunday adopted an anti-Islam policy in a manifesto that also demands curbs to immigration, as a poll showed it is now the country's third strongest party.

Formed only three years ago on a eurosceptic platform, the Alternative for Germany (AfD) has gained strength as the loudest protest voice against Chancellor Angela Merkel's welcome to refugees that brought in over one million asylum seekers last year.

With the migrant influx sharply down in recent months, the AfD has shifted focus to the signature issue of the xenophobic Pegida street movement, whose full name is Patriotic Europeans Against the Islamisation of the Occident.

"Islam is not part of Germany" ran a headline in the AfD policy paper agreed in a vote by some 2,400 members at the party congress in the western city of Stuttgart.

The paper demanded bans on minarets on mosques, the call to prayer, full-face veils for women and headscarves in schools.

A proposal for a more nuanced formulation -- to "stop Islamism but seek dialogue with Islam" -- was rejected with boos in the mostly-male gathering, which was held in a hall decorated with banners that read "Courage. Truth. Germany."

"Islam is in itself political," retorted one speaker, while another linked the religion with "sharia, suicide bombings and forced marriages".

More broadly, the AfD is presenting itself as a nationalistic conservative force that also questions climate change, promotes traditional gender roles and "family values", would reintroduce military conscription and take Germany out of the euro.

The weekend congress restated its hostility to the single currency, vowing to end "the euro experiment" via a referendum on whether or not Germany should remain in the eurozone.

The party meeting, which closed Sunday, also agreed a simplified tax system for its manifesto, notably aiming to ease the burden on those on low income and families.

Co-leader Joerg Meuthen said the AfD stood for a "modern conservatism" and a "healthy patriotism" while it rejected "the Germany of 1968, infected by the (socialist and environmentalist) red-green left".

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- 'Germany watching us' -

Having entered half of Germany's 16 state parliaments, the AfD -- seen as the country's answer to France's National Front and Austria's Freedom Party -- has now firmly set its sights on national elections next year.

"In the summer of 2015, they gave us up for dead," a triumphant AfD co-chair Frauke Petry told the delegates, declaring that the party does not intend to settle for the role of opposition group or junior coalition partner.

Instead, its new programme should allow the AfD "to win majorities", she told the gathering.

Support for the AfD stood at 13 percent, narrowly beating the ecologist Greens as Germany's third strongest party, according to an Emnid institute survey for the newspaper Bild am Sonntag.

The party has been at pains to distance itself from the hardcore far-right and neo-Nazi movements, which are a stubbornly persistent but fringe phenomenon in a country where collective shame over the Nazi era and the Holocaust runs deep.

Alexander Gauland, leader of the party in Brandenburg state in the former communist East, cautioned delegates to generally temper their statements and "keep in mind that all of Germany is watching us".

To drive home that message, the congress voted with 52 percent support to dissolve the Saarland regional party chapter because of its deep links with right-wing extremists groups.

To its many critics, however, the AfD represents xenophobia and a backward-looking isolationism.

On Saturday hundreds of anti-fascist demonstrators rallied outside the convention centre, with some burning tyres and hurling firecrackers.

In another act of harassment, a left-wing media site overnight published the names, addresses and telephone numbers of some 2,000 party members. AfD co-leader Joerg Meuthen pledged to file criminal charges against the unknown hackers behind the data leak.

Aside from drawing the anger of far-left groups, the AfD has also attracted near-universal condemnation from Germany's major parties.

The general secretary of Merkel's Christian Democrats, Peter Tauber, told the Bild am Sonntag newspaper: "The debates at the party congress show that the AfD wants to return to a Germany that never existed in that form.

"That isn't conservative, it's reactionary."