Leuthard enraged German politicians and campaigners when she argued that protesters petitioning for a reduction in air traffic volumes were like "the Taliban who are trying to sabotage Zürich airport“.
The transport minister told public broadcaster Schweizer Fernsehen that the words had popped out "in the heat of the debate" after she was drawn into a verbal spat on Monday with Volker Kauder, head of the German CDU's (Christian Democratic Union) parliamentary group.
Leuthard issued her apology after local authorities in Waldshut, where Kauder grew up on the Swiss-German border, informed the minister in a statement that “she should change her tune and pull in her horns".
Writing to Waldshut officials, Leuthard said she regretted her choice of wording but remained frustrated that negotiations had stalled, the TagesAnzeiger newspaper reports.
Volker Kauder and his fellow politician brother Siegfried have voiced support for a petition that has so far garnered 80,000 signatures to have the number of flights servicing Zürich curtailed.
The petition has angered Swiss politicians still seething after German officials in 2003 imposed a ban on late-night and weekend flights using its airspace to travel to and from Zurich airport.
With a number of south German politicians now urging further restrictions, the minister has expressed exasperation at what she views as a systematic reluctance on the German side to contribute to a constructive solution.