The anti-immigrant Alternative for Germany (AfD) maintained its slight lead over its "small party" competition, according to the latest poll reported by the German Bild am Sonntag newspaper on Sunday.

The "Sonntagstrend" survey by the polling institute Emnid showed support for the AfD at 11 percent, with the Left party just behind at 10 percent, followed by the business-friendly Free Democrats (FDP) at 9 percent and the Green party at 8 percent.

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Should the AfD's double-digit polling numbers hold, the populist party would enter Germany's national parliament for the first time after the September 24 election.

Another poll carried out by the Infratest dimap research institute last Thursday showed the AfD polling at 12 percent, but it should be noted that the margin of error can be up to plus or minus 3 percent.

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Merkel in comfortable lead, Schulz slipping

The Emnid poll also put German Chancellor Angela Merkel's conservatives well ahead of their Social Democratic Party (SPD) rivals and on track to remain the largest party in the Bundestag.

Support for Merkel's Christian Democratic Union (CDU) and their Bavarian sister party, the Christian Social Union (CSU), was at 36 percent.

The SPD, under party leader and chancellor candidate Martin Schulz, was polling at 22 percent in the poll.

When asked by pollsters about the success of the AfD, 58 percent said they believed Merkel's policies were partially responsible for the rise of the nationalist party while 34 percent disagreed.

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FDP, Greens vow to become third

The FDP and the Greens said on Sunday that the battle for third place was hardly over, with the Greens vowing to come out on top behind the CDU and SPD.

At the Greens' party conference in Berlin on Sunday, top candidate Kathrin Göring-Eckardt promised that the party "will land a real surprise coup" in the polls next week.

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Across town, FDP leader Christian Lindner begged to differ.

Speaking at the FDP's special party conference, Lindner said the Greens didn't have a chance of taking third place and that his party would need to step up as the main opposition voice should Merkel's CDU form another grand coalition with the SPD.

Lindner emphasized that the opposition shouldn't be led by the AfD, a party he described as having "nationalist-authoritarian" ideals.

The FDP is looking to re-enter the Bundestag after losing all of its seats when it didn't clear the 5 percent hurdle in the 2013 election.

The leaders of both parties did not rule out the option of a so-called "Jamaica coalition" between the Greens, the FDP and the CDU/CSU.