BERLIN (Reuters) - The German lower house of parliament’s administration has asked the far-right Alternative for Germany (AfD) for clarification about a potentially illegal donation from a Swiss firm, as a key party leader acknowledged mistakes in the handling of the money.

FILE PHOTO: Germany's anti-immigration party Alternative for Germany (AfD) leader Alexander Gauland attends a news conference after Bavaria state election, in Berlin, Germany, October 15, 2018. REUTERS/Michele Tantussi/File Photo

Alexander Gauland, one of the party’s leaders, told mass-circulation daily Bild that the treasurer of an AfD branch on Lake Constance, where his co-leader Alice Weidel ran for office last year, had “clearly acted improperly.”

“I don’t think she (Weidel) has to blame herself,” Gauland said in an interview to be published Tuesday. “But it’s a stupid problem. The treasurer clearly acted improperly. The money was paid back too late; I freely admit that.”

The latest scandal to engulf the anti-immigrant party erupted this week after the Sueddeutsche Zeitung newspaper and broadcasters NDR and WDR reported that Weidel’s AfD branch had received 130,000 euros ($145,000) in potentially illegal donations from a Swiss firm called PWS in September 2017.

The funds were returned by the party months later, party officials told German media.

Weidel told Bild she would have taken action sooner if she had suspected the donations to be problematic. “If I had suspected then that the assessment of the state treasurer was wrong, I would have naturally intervened.”

A party spokesman said the money was returned to the Swiss firm after doubts arose about the legality. Weidel told broadcaster ZDF that she first learned of the donation in September 2017, but relied on the treasurer’s judgment.

The administration for the Bundestag lower house said party donations from countries outside the European Union must not be accepted as a matter of principle, and illegal donations needed to be transferred back or paid to the Bundestag president.

“The (AfD’s) federal party association has today been asked to comment on the urgent questions that have been raised,” the Bundestag administration said in a statement.

The AfD could face significant financial penalties for accepting the donation and failing to pay it back promptly, legal experts said. The incident has also triggered calls for Weidel’s resignation.

Wolfgang Kubicki, a member of the opposition Free Democrats and a vice president of the parliament, told the Funke Mediengruppe newspaper chain that Weidel and other party leaders should have known the donation could not be accepted. He said the party faced fines of up to 390,000 euros as a result of the incident, depending on the outcome of the parliamentary probe.

The anti-immigrant AfD entered the national parliament for the first time last year, winning around 13 percent of the vote.

Johannes Kahrs, a Social Democrat, told newspaper Handelsblatt that Weidel should resign if the donation was deemed to be have been illegal.