BERLIN (Reuters) - A regional parliament has lifted the immunity of the best known politician in the anti-immigration Alternative for Germany (AfD) party, opening the way for prosecutors to pursue possible perjury charges against her.

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Frauke Petry, who is the AfD’s co-chairwoman, has been dogged by allegations that she lied under oath to a committee of the Saxony parliament about how the party’s campaign for the 2014 election in the state was financed.

The ending of her immunity from prosecution adds to the right-wing party’s problems less than four weeks before a national election. Weakened by infighting, it has bled support over the last year as voters’ concerns about immigration have eased.

Prosecutors have pursued the case against Petry, who denies the allegations, for more than a year.

Her immunity as a member of the Saxony’s parliament ended at midnight, a spokesman for the assembly said.

A spokesman for prosecutors in the state capital Dresden said they would await written confirmation of that from the parliament’s president before any further proceedings could be agreed upon.

The AfD is polling between 7 and 10 percent in opinion surveys - well down from a high of 15.5 percent at the end of 2016 but still clearing the 5-percent threshold needed to enter the federal parliament in the Sept. 24 national election.

Petry cuts an increasingly isolated figure in the AfD, which she transformed from an anti-euro party at its founding in 2013 into a group that taps into voters’ concerns about migration.

The party soared in the polls after Chancellor Angela Merkel’s decision in 2015 to open Germany’s borders to migrants fleeing war and poverty in the Middle East and beyond, of whom more than a million have since arrived.

At a party conference in April, Petry suffered a humiliating defeat when delegates refused to discuss her plan to shift the party towards the mainstream.