BERLIN (Reuters) - The anti-immigrant Alternative for Germany (AfD) is set to storm into three state parliaments by winning up to 18 percent in Sunday’s regional elections, a poll showed, in what would be a big setback for Chancellor Angela Merkel and her open-door refugee policy.

A little flag and brochures of the right-wing Alternative for Germany (AFD) are pictured during a rally for the upcoming Saxony-Anhalt state elections in Bitterfeld, Germany, February 29, 2016. REUTERS/Fabrizio Bensch

The elections in the states of Saxony-Anhalt, Baden-Wuerttemberg and Rhineland-Palatinate are the first in Germany since the refugee crisis began and will give voters a chance to punish or reward parties for their role in or response to the influx of more than a million migrants last year.

The poll for broadcaster ZDF showed the AfD would probably win 18 percent of the vote in the eastern state of Saxony-Anhalt, up one point from the same survey last week, putting it on course to be the third biggest political force there after Merkel’s Christian Democrats (CDU) and the far-left Linke.

Eleven percent of voters in the industrial heartland region of Baden-Wuerttemberg are poised to vote for the right-wing AfD while the Greens are set to be the strongest performer there with 32 percent, followed by the CDU on 29 percent - down one point compared with the same poll last week.

In the wine-growing region of Rhineland-Palatinate 9 percent are set to give their vote to the AfD in a move that would make it the third biggest party there.

The Social Democrats (SPD) - the junior coalition partner to Merkel’s CDU at the federal level - are set to remain the biggest party in Rhineland-Palatinate with 36 percent, with the CDU close on its heels at 35 percent.

The AfD is already represented in five of Germany’s 16 regional parliaments but the party, which was originally founded as an anti-euro party in 2013, is not yet present in any of the state assemblies that will be elected on Sunday.

The three states have a combined population of some 17 million, around a fifth of Germany’s 81 million.

The AfD, which has used slogans such as “Secure the borders! Stop the asylum chaos!” has benefitted from growing concerns among Germans about migrant numbers and the country’s ability to integrate vast numbers of people with different cultures.

The party, whose leader stirred controversy by suggesting that migrants trying to enter Germany illegally should be shot if necessary, has eaten away at support for the established parties in Germany and could make it harder for them to form stable coalition governments.