Berlin (CNN) The leadership of the hardline Alternative for Germany party was in disarray Monday, a day after its historic breakthrough in the German elections delivered a stinging blow to Chancellor Angela Merkel's authority.

At a press conference in Berlin that was intended to burnish the AfD's success, its chairwoman Frauke Petry walked out. She declared that she would not sit with the party in the Bundestag and said it had to address dissent within its own ranks.

The AfD won 13% of the vote and came a stunning third place behind the main center-right and center-left parties.

It polled particularly strongly in the former East Germany, which includes Berlin, attracting 21.5% of the vote, according to exit polling conducted by Infratest Dimap. In the West, it scored about 11%, the projections said. The results put the AfD on course to become the second largest party in the east, after the CDU.

The AfD becomes the first far-right party to enter the Bundestag since 1961. But it has been riven with internal strife: Petry has been regarded as a more moderate force in the party, arguing that it had to break with the far right in order to move from opposition into government.

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