BERLIN (Reuters) - Frauke Petry, co-leader of the far-right Alternative for Germany, said on Tuesday she was leaving the party in a major blow to its credibility just two days after it surged to third place in a national election.

Frauke Petry, chairwoman of the anti-immigration party Alternative fuer Deutschland (AfD) speaks as she leaves a news conference in Berlin, Germany, September 25, 2017. REUTERS/Fabrizio Bensch

The anti-immigrant AfD won 12.6 percent of the vote in Germany’s election on Sunday, becoming the third-largest group in parliament and the first from the far-right to win seats in the Bundestag since the 1950s.

Petry, the highest-profile figure in the AfD’s more moderate wing, had shocked other senior members by saying on Monday she would not sit with the AfD in the Bundestag (lower house) but rather as an independent member of parliament. Her husband, another senior AfD figure, is also leaving the party.

“We tried to change course but you have to realize when you reach a point when that is no longer possible,” Petry, a 42-year-old chemist, told reporters in the eastern city of Dresden. “I have five children for whom I am responsible and ultimately you have to be able to look yourself in the mirror.”

Petry has clashed with other senior members, arguing for the party to take a more moderate course to make it possible for it to join a coalition government.

Her husband, Marcus Pretzell - head of the AfD in the western state of North Rhine-Westphalia (NRW) and also an MP in the European Parliament - is quitting the party and will become an independent MP, a spokesman for the AfD in NRW said.

The spokesman said Pretzell and another AfD lawmaker in NRW’s regional assembly who is also leaving the party had made the decision for reasons of “personal integrity”.

On Monday, four of the 17 AfD lawmakers in the assembly of the eastern state of Mecklenburg-Vorpommern announced they were bolting because the party had become more radical.

Europe’s far-right parties have a history of infighting among their various factions. Marine Le Pen, leader of France’s National Front, last week lost her deputy over policy differences.

“SURPRISE STEP”

Alexander Gauland and Alice Weidel, the AfD’s top candidates during the election campaign, were elected as chairs of the party’s parliamentary group on Tuesday.

Gauland is a supporter of Bjoern Hoecke, a senior AfD member who has courted controversy by denying that Adolf Hitler was “absolutely evil” and calling Berlin’s Holocaust Memorial a “monument of shame”. Weidel was originally an opponent of Hoecke but has not been so critical of him lately.

Weidel said she did not expect other lawmakers to quit the party but added: “We’ll have to see. The step surprised us all, but there are not yet any trends recognizable in the future parliamentary group.”

Senior AfD member Dirk Driesang, who in July founded a moderate group within the AfD called the “Alternative Centre”, with which Petry was said to sympathize, told news magazine Der Spiegel that the group could not understand Petry’s decision and would not be following in her footsteps.

He said the group would continue to fight for the AfD to take a moderate course and added that “a spin-off from the AfD is a stillbirth”. Driesang pointed to the example of Bernd Lucke, who founded the AfD then left in 2015 due to what he saw as rising xenophobia and then formed a new, unsuccessful party.

Petry was the most recognizable face in the AfD during its swift rise over the past two years. But she said on Monday she could not stand with an “anarchistic party” that lacked a credible plan to govern.

For months, Petry has urged the AfD to soften its stance and prepare to join coalition governments, while others wanted the party to stick to opposition. Mainstream parties refuse to work with the AfD.

She had also distanced herself from some of the AfD’s more radical senior members, saying their comments were putting voters off.

Gauland caused a scandal during the election campaign by saying Germans should be proud of their World War Two soldiers. He also said the integration minister should be “disposed of” in Turkey, where her parents come from.

As the AfD convened in Berlin on Tuesday for its first parliamentary group meeting, Gauland said discussions in the Bundestag would not echo those of the party’s campaign.

“It’s clear that the talks during the campaign are different to those held in parliament,” he said.